The DOI matches its Crossref record; 64 of the 65 references it cites were found in a registry or an index.
Does Conflict Beget Conflict? Explaining Recurring Civil War
Abstract
This article attempts to explain why some countries experience civil wars while others do not. It argues that renewed war is likely to have less to do with the attributes of a previous war, as many people have argued, than with current incentives individual citizens have to rejoin a rebel group. Civil wars will have little chance to get off the ground unless individual farmers, shopkeepers, and potential workers choose to enlist in the rebel armies that are necessary to pursue a war, and enlistment is only likely to be attractive when two conditions hold. The first is a situation of individual hardship or severe dissatisfaction with one’s current situation. The second is the absence of any nonviolent means for change. An analysis of all civil wars ending between 1945 and 1996 suggests that a higher quality of life and greater access to political participation have a significant negative effect on the likelihood of renewed war. Countries that provide higher levels of economic well-being to their citizenry and create an open political system are less likely to experience multiple civil wars regardless of what happened in a previous conflict.
Overview
Integrity signals
Registry
Cites
Statistics
Verification
Claims the paper makes
Claims other papers make about this one
Each is checked against this paper’s own text: does it say what the citing paper says it does?
In the citing paper
“actors who have incentives to initiate violence will find the conditions more conducive to radicalization and mobilization in poor, post-conflict societies (22,185).”
From Vicious Circles: Violence, Vulnerability, and Climate Change (2021) · cites this paper as [185]
In the citing paper
“Grievances are important because they provide rebel leaders with an opportunity to mobilize potential soldiers and supporters who are dissatisfied with the government (Walter 2004, 374-75).”
From Conflict Recurrence and Postconflict Justice: Addressing Motivations and Opportunities for Sustainable Peace (2017) · cites this paper as Walter 2004
In the citing paper
“Recruitment and civilian support, in turn, are essential for the opposition to resume violence against the government as it bolsters their fighting capabilities.”
From Conflict Recurrence and Postconflict Justice: Addressing Motivations and Opportunities for Sustainable Peace (2017) · cites this paper as Walter 2004
Citations
Cites
Ethnicity, Insurgency, and Civil War
FEARON, J. D., & LAITIN, D. D. (2003) · American Political Science Review · doi:10.1017/s0003055403000534 · Cited by 7,366
Threshold models of collective behavior
Granovetter, M. (1978) · American Journal of Sociology · doi:10.1086/226707 · Cited by 6,072
From Mobilization to Revolution
Stearns, P. N., & Tilly, C. (1979) · The American Historical Review · doi:10.2307/1855671 · Cited by 4,583
Natural Resource Abundance and Economic Growth
Sachs, J., & Warner, A. (1995) · doi:10.3386/w5398 · Cited by 4,461
From Mobilization to Revolution
Tilly, C. (2017) · Routledge eBooks · doi:10.4324/9781315205021-5 · Cited by 4,010
(1970) · Medical Entomology and Zoology · Cited by 3,500
Making the most of statistical analyses: improving interpretation and presentation
King, G., Tomz, M., & Wittenberg, J. (2000) · American Journal of Political Science · doi:10.2307/2669316 · Cited by 3,232
Taking Time Seriously: Time-Series-Cross-Section Analysis with a Binary Dependent Variable
Beck, N. L., Katz, J. N., & Tucker, R. P. (1998) · American Journal of Political Science · doi:10.2307/2991857 · Cited by 2,443
Toward a Democratic Civil Peace? Democracy, Political Change, and Civil War, 1816–1992
Hegre, H. (2001) · American Political Science Review · doi:10.1017/s0003055401000119 · Cited by 1,604
Tracking Democracy's Third Wave with the Polity III Data
Jaggers, K., & Gurr, T. R. (1995) · Journal of Peace Research · doi:10.1177/0022343395032004007 · Cited by 1,332
Flagged first, then by citations
1 of the 65 references couldn’t be matched to a known paper.
Research works printed but not linked: 5
- 2001, ‘Civil Wars and Poverty: The Role of External Interventions, Political Rights and Economic Growth’
- 1972, ‘War Power and the Willingness to Suffer’, 167
- 2003, ‘Resources and Rebellion in Aceh, Indonesia’
- 1993, ‘The Causes of Peace’, 235
- 2004, ‘War as a Reputation Problem’
Cited by
Sorted by citations
Items 101–200 of 686
The Lancet Commission on peaceful societies through health equity and gender equality
Percival, V., Thoms, O. T., Oppenheim, B., Rowlands, D., Chisadza, C., Fewer, S., Yamey, G., Alexander, A. C., Allaham, C. L., Causevic, S., et al. (2023) · The Lancet · doi:10.1016/s0140-6736(23)01348-x · Cited by 55
Tolerating Threat? The Independent Effects of Civil Conflict on Domestic Political Tolerance
Hutchison, M. L. (2013) · Journal of Conflict Resolution · doi:10.1177/0022002713478566 · Cited by 51
Pietraszewski, D. (2016) · Evolution and Human Behavior · doi:10.1016/j.evolhumbehav.2016.04.006 · Cited by 55
Civil war recurrence and postwar violence: Toward an integrated research agenda
Bara, C., Deglow, A., & van Baalen, S. (2021) · European Journal of International Relations · doi:10.1177/13540661211006443 · Cited by 50
Quinn, J., Joshi, M., & Melander, E. (2019) · International Studies Quarterly · doi:10.1093/isq/sqz073 · Cited by 49
Dilemmas of Energy Transitions in the Global South
Kumar, A., Höffken, J. I., & Pols, A. J. K. (2021) · Routledge eBooks · doi:10.4324/9780367486457 · Cited by 55
Explaining Recidivism of Ex-Combatants in ColombiaPreprint
Kaplan, O., & Nussio, E. (2013) · SSRN Electronic Journal · doi:10.2139/ssrn.2350318 · Cited by 48
Taylor, L. K., Merrilees, C. E., Goeke‐Morey, M. C., Shirlow, P., Cairns, E., & Cummings, E. M. (2014) · Social Development · doi:10.1111/sode.12074 · Cited by 50
Humanitarian Assistance and the Duration of Peace after Civil War
Narang, N. (2014) · The Journal of Politics · doi:10.1017/s0022381613001382 · Cited by 50
Rebel Natural Resource Exploitation and Conflict Duration
Conrad, J. M., Greene, K. T., Walsh, J. I., & Whitaker, B. E. (2018) · Journal of Conflict Resolution · doi:10.1177/0022002718755853 · Cited by 47
Financing the peace: Evaluating World Bank post-conflict assistance programs
Flores, T. E., & Nooruddin, I. (2008) · The Review of International Organizations · doi:10.1007/s11558-008-9039-0 · Cited by 50
Legislative Gender Diversity and the Resolution of Civil Conflict
Best, R. H., Shair‐Rosenfield, S., & Wood, R. M. (2018) · Political Research Quarterly · doi:10.1177/1065912918785459 · Cited by 48
The Rebels’ Credibility Dilemma
Thomas, J., Reed, W., & Wolford, S. (2016) · International Organization · doi:10.1017/s0020818316000175 · Cited by 44
The Rule of Law in Post-Conflict Settings: The Empirical Record
Haggard, S. M., & Tiede, L. B. (2013) · International Studies Quarterly · doi:10.1111/isqu.12103 · Cited by 45
‘Can’t buy me legitimacy’: the elusive stability of Mideast rentier regimes
Abulof, U. (2015) · Journal of International Relations and Development · doi:10.1057/jird.2014.32 · Cited by 42
Why Ethnic Subaltern-Led Parties Crowd Out Armed Organizations: Explaining Maoist Violence in India
Chandra, K., & García‐Ponce, O. (2019) · World Politics · doi:10.1017/s004388711800028x · Cited by 41
Poverty and Violent Conflict: A Micro‐Level Perspective on the Causes and Duration of Warfare
Justino, P. (2011) · IDS Working Papers · doi:10.1111/j.2040-0209.2011.00385_2.x · Cited by 41
McRae, D. (2013) · BRILL eBooks · doi:10.1163/9789004251724 · Cited by 41
Introducing xSub: A new portal for cross-national data on subnational violence
Zhukov, Y., Davenport, C., & Kostyuk, N. (2019) · Journal of Peace Research · doi:10.1177/0022343319836697 · Cited by 43
Chiba, D., Metternich, N. W., & Ward, M. D. (2015) · Political Science Research and Methods · doi:10.1017/psrm.2014.46 · Cited by 39
Predicting violence within genocide: A model of elite competition and ethnic segregation from Rwanda
McDoom, O. S. (2014) · Political Geography · doi:10.1016/j.polgeo.2014.05.006 · Cited by 44
Karlén, N. (2017) · Journal of Peace Research · doi:10.1177/0022343317700465 · Cited by 40
Identifying Pathways to Peace: How International Support Can Help Prevent Conflict Recurrence
Mroß, K., Fiedler, C., & Grävingholt, J. (2021) · International Studies Quarterly · doi:10.1093/isq/sqab091 · Cited by 39
The Arab Spring. A Quantitative Analysis
Korotayev, A., Issaev, L. M., Malkov, S., & Романовна, Ш. А. (2022) · Societies and political orders in transition · doi:10.1007/978-3-030-86468-2_30 · Cited by 39
How War Changes Land: Soil Fertility, Unexploded Bombs, and the Underdevelopment of Cambodia
Lin, E. (2020) · American Journal of Political Science · doi:10.1111/ajps.12577 · Cited by 40
International Multiparty Mediation and Conflict Management
Vuković, S. (2015) · Routledge eBooks · doi:10.4324/9781315749969 · Cited by 38
Aber, J. L., Dolan, C. T., Torrente, C. E., Halpin, P. F., Johnston, B., Starkey, L., Shivshanker, A., Annan, J. R., Seidman, E., & Wolf, S. (2016) · Development and Psychopathology · doi:10.1017/s0954579416001139 · Cited by 44
The Internationalization of Ethnic Conflict: State, Society, and Synthesis
Carment, D., James, P., & Taydaş, Z. (2009) · International Studies Review · doi:10.1111/j.1468-2486.2008.01825.x · Cited by 38
Pietraszewski, D. (2022) · Behavioral and Brain Sciences · doi:10.1017/s0140525x21000583 · Cited by 45
War termination and women's political rights.
Joshi, M., & Olsson, L. (2021) · Social Science Research · doi:10.1016/j.ssresearch.2020.102523 · Cited by 23
The Impact of Armed Civil Conflict on Household Welfare and Policy Responses
Justino, P. (2011) · doi:10.5040/9781849665872.ch-002 · Cited by 37
Termination and Recurrence of Civil War: Which Outcomes Lead to Durable Peace after Civil War?
Ohmura, H. (2011) · Japanese Journal of Political Science · doi:10.1017/s146810991100017x · Cited by 40
Civil Conflicts Abroad, Foreign Fighters, and Terrorism at Home
Braithwaite, A., & Chu, T. S. (2017) · Journal of Conflict Resolution · doi:10.1177/0022002717707304 · Cited by 36
The Last mile in ending extreme poverty
(2015) · Choice Reviews Online · doi:10.5860/choice.193778 · Cited by 36
von Kaltenborn-Stachau, H. (2008) · World Bank, Washington, DC eBooks · doi:10.1596/28229 · Cited by 35
Oil Wealth, Post-conflict Elections, and Postwar Peace Failure
Keels, E. (2015) · Journal of Conflict Resolution · doi:10.1177/0022002715595702 · Cited by 36
Twenty Years After Dayton: Bosnia-Herzegovina (Still) Stable and Explosive
Kartsonaki, A. (2016) · Civil Wars · doi:10.1080/13698249.2017.1297052 · Cited by 35
Poverty and Violent Conflict: A Micro-Level Perspective on the Causes and Duration of WarfarePreprint
Justino, P. (2008) · SSRN Electronic Journal · doi:10.2139/ssrn.1142802 · Cited by 35
Blattman, C., & Miguel, E. A. (2009) · National Bureau of Economic Research · doi:10.3386/w14801 · Cited by 39
Economic Development in Peacekeeping Host Countries
Bove, V., & Elia, L. (2017) · CESifo Economic Studies · doi:10.1093/cesifo/ifx009 · Cited by 36
Control, Coercion, and Cooptation
Liu, S. (2021) · World Politics · doi:10.1017/s0043887121000174 · Cited by 41
Emigrants and the onset of civil war
Miller, G. L., & Ritter, E. H. (2013) · Journal of Peace Research · doi:10.1177/0022343313505302 · Cited by 32
To instill fear or love: Terrorist groups and the strategy of building reputation
Akcinaroglu, S., & Tokdemir, E. (2016) · Conflict Management and Peace Science · doi:10.1177/0738894216634292 · Cited by 32
Learning in the chaos: A political economy analysis of education in Afghanistan
Pherali, T. J., & Sahar, A. (2018) · Research in Comparative and International Education · doi:10.1177/1745499918781882 · Cited by 32
Wennmann, A. (2005) · Security Dialogue · doi:10.1177/0967010605060450 · Cited by 32
Pacifism and the ethical imagination in IR
Jackson, R. (2017) · International Politics · doi:10.1057/s41311-017-0137-6 · Cited by 31
Institutions and Ethnic Trust: Evidence from Bosnia
Whitt, S. (2010) · Europe Asia Studies · doi:10.1080/09668130903506839 · Cited by 31
Wood, R. M., & Kathman, J. D. (2012) · SSRN Electronic Journal · Cited by 31
Community Counts: The Social Reintegration of Ex-Combatants in ColombiaPreprint
Kaplan, O., & Nussio, E. (2012) · SSRN Electronic Journal · doi:10.2139/ssrn.2138188 · Cited by 31
Watts, S., Johnston, T., Lane, M., Mann, S., McNerney, M., & Brooks, A. (2018) · RAND Corporation eBooks · doi:10.7249/rr2447 · Cited by 30
Gialloreti, L. E., Basa, F. B., Moramarco, S., Salih, A. O., Alsilefanee, H. H., Qadir, S. A., Bezenchek, A., Incardona, F., Giovanni, D. D., Khorany, R., et al. (2020) · Frontiers in Public Health · doi:10.3389/fpubh.2020.00007 · Cited by 30
Sustaining the peace after ethnic civil wars
Gurses, M., & Rost, N. (2013) · Conflict Management and Peace Science · doi:10.1177/0738894213499667 · Cited by 30
Pro-regime Militias and Civil War Duration
Aliyev, H. (2017) · Terrorism and Political Violence · doi:10.1080/09546553.2017.1393415 · Cited by 29
Principles of Conflict Economics: A Primer for Social Scientists
Anderton, C. H., & Carter, J. R. (2009) · Cited by 31
Civil war termination and foreign direct investment, 1989–2012
Joshi, M., & Quinn, J. (2018) · Conflict Management and Peace Science · doi:10.1177/0738894218778260 · Cited by 30
A Typology of Post-Conflict Environments
Brown, G. K., Langer, A., & Stewart, F. (2011) · Lirias · Cited by 28
Post-conflict economic recovery
Pabst, H. F. (2013) · University of Vienna · doi:10.25365/thesis.30381 · Cited by 27
CTS, counterterrorism and non-violence
Jackson, R. (2017) · Critical Studies on Terrorism · doi:10.1080/17539153.2017.1334851 · Cited by 26
The Supply and Demand of Rebel Governance
Florea, A., & Malejacq, R. (2023) · International Studies Review · doi:10.1093/isr/viae004 · Cited by 26
‘Together at the Heart’: Familial Relations and the Social Reintegration of Ex-combatants
Suárez, C., & Baines, E. K. (2021) · International Peacekeeping · doi:10.1080/13533312.2021.1952408 · Cited by 30
Joshi, M. (2015) · BMC International Health and Human Rights · doi:10.1186/s12914-015-0066-7 · Cited by 26
Immigration and Political Instability
Gebremedhin, T. A., & Mavisakalyan, A. (2013) · Kyklos · doi:10.1111/kykl.12024 · Cited by 26
Poverty and Civil War: What Policymakers Need to KnowPreprint
Rice, S. E., Graff, C., & Lewis, J. I. (2006) · SSRN Electronic Journal · doi:10.2139/ssrn.1015091 · Cited by 26
Violent Conflict and Human Capital AccumulationPreprint
Justino, P. (2011) · SSRN Electronic Journal · doi:10.2139/ssrn.1948651 · Cited by 26
Manpower to coerce and co-opt—State capacity and political violence in southern Sudan 2006–2010
Juan, A. D., & Pierskalla, J. H. (2014) · Conflict Management and Peace Science · doi:10.1177/0738894213520393 · Cited by 25
Territorial Dimensions of Enduring Internal Rivalries
Fuhrmann, M., & Tir, J. (2009) · Conflict Management and Peace Science · doi:10.1177/0738894209106478 · Cited by 25
The Impact of Armed Civil Conflict on Household Welfare and Policy
Justino, P. (2011) · IDS Working Papers · doi:10.1111/j.2040-0209.2011.00384_2.x · Cited by 25
Lockyer, A. (2008) · The Sydney eScholarship Repository (The University of Sydney) · Cited by 25
When Do Disarmament, Demobilization and Reintegration Programs Succeed?Preprint
Banholzer, L. (2013) · SSRN Electronic Journal · doi:10.2139/ssrn.2367307 · Cited by 29
Mixed regimes and political violence in Africa
Goldsmith, A. A. (2010) · The Journal of Modern African Studies · doi:10.1017/s0022278x10000315 · Cited by 24
Negotiating justice: Ceasefires, peace agreements, and post-conflict justice
Cox, J. M. (2019) · Journal of Peace Research · doi:10.1177/0022343319879485 · Cited by 24
The business of peace: understanding corporate contributions to conflict management
Melin, M. M. (2020) · International Interactions · doi:10.1080/03050629.2020.1723581 · Cited by 24
The paradox of power-sharing: stability and fragility in postwar Lebanon
Rizkallah, A. (2017) · Ethnic and Racial Studies · doi:10.1080/01419870.2017.1277031 · Cited by 24
From Insurgent to Incumbent: State Building and Service Provision After Rebel Victory in Civil Wars
Thaler, K. M. (2018) · Digital Access to Scholarship at Harvard (DASH) (Harvard University) · Cited by 24
Enforcement of sexual violence law in post-civil conflict societies
Haglund, J., & Richards, D. L. (2017) · Conflict Management and Peace Science · doi:10.1177/0738894217695536 · Cited by 23
Conflict-Related Sexual Violence and the Re-Escalation of Lethal Violence
Nagel, R. (2020) · International Studies Quarterly · doi:10.1093/isq/sqaa086 · Cited by 10
Rebel institutions and negotiated peace
Albert, K. E. (2023) · Conflict Management and Peace Science · doi:10.1177/07388942221147508 · Cited by 23
Micro-Level Dynamics of Conflict, Violence, and Development: A New Analytical Framework
Justino, P., Brück, T., & Verwimp, P. (2013) · Oxford University Press eBooks · doi:10.1093/acprof:oso/9780199664597.003.0001 · Cited by 23
Mobilization and Conflict in Multiethnic States
Vogt, M. (2019) · doi:10.1093/oso/9780190065874.001.0001 · Cited by 24
Social Norms in the Aftermath of Ethnic Violence
Whitt, S. (2012) · Journal of Conflict Resolution · doi:10.1177/0022002712459714 · Cited by 22
The Impact of Armed Civil Conflict on Household Welfare and Policy ResponsesPreprint
Justino, P. (2009) · SSRN Electronic Journal · doi:10.2139/ssrn.1425043 · Cited by 23
Destroying Trust in Government: Effects of a Broken Pact among Colombian Ex-Combatants
Kreutz, J., & Nussio, E. (2019) · International Studies Quarterly · doi:10.1093/isq/sqz058 · Cited by 22
On the Links Between Violent Conflict and Household Poverty: How Much do We Really Know?Preprint
Justino, P. (2008) · SSRN Electronic Journal · doi:10.2139/ssrn.1116265 · Cited by 22
Seeds of Distrust: Conflict in UgandaPreprint
Rohner, D., Thoenig, M., & Zilibotti, F. (2011) · SSRN Electronic Journal · doi:10.2139/ssrn.1972310 · Cited by 22
A Few Poorly Organized Men: Interreligious Violence in Poso, Indonesia
McRae, D. (2013) · Cited by 22
Grimm, S., & Mathis, O. L. (2015) · Europe Asia Studies · doi:10.1080/09668136.2015.1055237 · Cited by 21
Peasants, Patrons, and Parties: The Tension between Clientelism and Democracy in Nepal1
Joshi, M., & Mason, T. D. (2011) · International Studies Quarterly · doi:10.1111/j.1468-2478.2010.00639.x · Cited by 21
Collective Deterrence in the Shadow of Shifting Power
Phillips, J., & Wolford, S. (2021) · International Studies Quarterly · doi:10.1093/isq/sqaa095 · Cited by 20
Do International Organizations Reduce the Risk of Crisis Recurrence?
Bakaki, Z. (2018) · Journal of Global Security Studies · doi:10.1093/jogss/ogy012 · Cited by 20
Seeds of peace? Land reform and civil war recurrence following negotiated settlements
Keels, E., & Mason, T. D. (2018) · Cooperation and Conflict · doi:10.1177/0010836717750201 · Cited by 20
Gromes, T., & Ranft, F. (2021) · Civil Wars · doi:10.1080/13698249.2022.2004043 · Cited by 19
The Contagion of Interstate Violence
Li, M., Leidner, B., Euh, H., & Choi, H. (2016) · Personality and Social Psychology Bulletin · doi:10.1177/0146167216649609 · Cited by 19
Reconciliation and Development
Brounéus, K. (2008) · Springer eBooks · doi:10.1007/978-3-540-85754-9_8 · Cited by 19
Reeder, B. W., & Polizzi, M. S. (2021) · International Studies Quarterly · doi:10.1093/isq/sqab018 · Cited by 6
Why Is Mediation So Hard? The Case of Syria
Crocker, C. A., Hampson, F. O., Aall, P., & Palamar, S. (2014) · Springer eBooks · doi:10.1007/978-3-319-10687-8_11 · Cited by 18
State Capacity, Regime Type, and Sustaining the Peace after Civil War
Mason, T. D., & Greig, J. M. (2016) · International Interactions · doi:10.1080/03050629.2017.1260012 · Cited by 18
Mroß, K. (2018) · International Peacekeeping · doi:10.1080/13533312.2018.1557052 · Cited by 18
Government-Sponsored Mass Killing and Civil War Reoccurrence
Uzonyi, G., & Hanania, R. (2017) · International Studies Quarterly · doi:10.1093/isq/sqx050 · Cited by 19
Families and Foes: Ethnic Civil War Duration.
Kirschner, S. A. (2009) · Deep Blue (University of Michigan) · Cited by 17
Shared Societies and Armed Conflict: Costs, Inequality and the Benefits of Peace
Justino, P. (2012) · IDS Working Papers · doi:10.1111/j.2040-0209.2012.00410.x · Cited by 19
Metadata
- Authors
- Walter, B. F.
- Affiliations
- University of California San Diego (US)
- Corresponding author
- Walter, Barbara F
- ORCID
- Walter, Barbara F
- Venue
- Journal of Peace Research
- Publisher
- Oxford University Press (OUP)
- Published
- 2004-05-01
- Volume
- 41
- Issue
- 3
- Pages
- 371-388
- ISSN
- 0022-3433 (ISSN-L)
- 1460-3578
- OpenAlex
- W2115057879
- Cited by
- 690
- References
- 65
- Citations by year
- 2026: 30 · 2025: 19 · 2024: 37 · 2023: 52 · 2022: 48 · 2021: 53 · 2020: 41 · 2019: 43 · 2018: 48 · 2017: 33 · 2016: 29 · 2015: 28 · 2014: 31 · 2013: 36 · 2012: 35
- FWCI
- 31.68
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Journal of Peace Research (publishedVersion)
- RePEc: Research Papers in Economics (submittedVersion)
- Topics
- Social Sciences › Sociology and Political Science › Political Conflict and Governance
- Social Sciences › Sociology and Political Science › Peacebuilding and International Security
- Social Sciences › Economics, Econometrics and Finance › General Economics, Econometrics and Finance › Natural Resources and Economic Development
- Keywords
- civil war recurrence, economic well-being, political participation, quality of life, civil war onset
About these checks
Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.
Statistics and arithmetic are recomputed, not judged.
Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.
What counts as a claim ›How we measure confidence ›How we check this ›
Are you an author, or do you see a problem with this page? Request a review