Peace
Why is there war?
Wars rarely have just one cause. How research defines war, which causes it names and why most wars since 1945 have been fought within states
Key points at a glance
- Wars rarely have just one cause. Research names weak states, disputes over resources and the decisions of those involved.
- One school sees wars as a by-product of social upheaval, another as the result of deliberate decisions.
- Between 1945 and 2020 AKUF counted 242 wars, about 70% of them fought within states.
- Whether a conflict counts as a war depends on the definition, for UCDP on at least 1,000 battle deaths in a year.
- For prevention, the German government follows guidelines that give priority to civilian means such as mediation.
In numbers
242
wars
between 1945 and 2020, counted by AKUF
70%
of them intrastate
170 of the 242 wars
1,000
battle deaths a year
from here on UCDP speaks of war
- intrastate wars170
- interstate and other wars72
Systemic approach
- Looks at
- the structures of a society
- War is
- a by-product of social, economic and political upheaval
- Key question
- Which upheavals make violence likely?
Strategic approach
- Looks at
- the people who decide
- War is
- the result of calculations in which individuals, staffs, groups or authorities decide to take up arms
- Key question
- Why does someone decide to use violence?
- AKUF
- war as a violent mass conflict with three features
- UCDP
- armed conflict from 25 battle deaths in a calendar year
- HIIK
- five levels of intensity from dispute to war
- Two schools
- systemic and strategic approach
Why is there war?
There is no single answer to this question. Research on the causes of war has traditionally distinguished two schools, which emphasise different things when looking at the same war.
One takes a systemic approach. In its view, wars are a by-product of social, economic and political upheaval. The other school takes a strategic or decision-theoretical approach and understands wars as the result of calculations, that is, of weighing up and deciding.
The two views do not exclude each other. The following sections show how research defines war in the first place, which causes it highlights and why most wars since 1945 have taken place within states.
What counts as a war?
AKUF, the Working Group on the Causes of War at the University of Hamburg, defines war, following István Kende, as a violent mass conflict with three features. Two or more armed forces take part in the fighting, with regular government forces on at least one side. Both sides are centrally organised to a minimum degree, and the fighting takes place with a certain continuity, not only as occasional, spontaneous clashes.
UCDP, the Uppsala Conflict Data Program at Uppsala University, counts a state-based armed conflict from 25 battle-related deaths in a calendar year. At least one side is the government of a state, and the conflict concerns government or territory. UCDP only lists a conflict as a war from 1,000 battle-related deaths in a calendar year.
HIIK, the Heidelberg Institute for International Conflict Research, starts earlier. It already understands a political conflict as a difference in positions between at least two actors and distinguishes five levels of intensity, from dispute to war. When you read figures on wars, it is therefore always worth asking which definition was used to count them.
Which causes does research name?
For conflicts within states, the weakness of the state is regarded as the main cause. One view, which Daniel Lambach sets out for the Federal Agency for Civic Education (bpb), is this: intrastate conflicts arise especially often where the state is unable to stop the violence of competing actors.
According to an account by the Federal Agency for Civic Education from 2018, the struggle for resources has by now become the second most common cause of conflict. In 2017, it says, resources played a decisive role in 17 of 36 high-intensity violent conflicts. It too says that the causes are usually complex, and that scarcity or abundance of resources alone is only very rarely the cause of conflict.
None of these causes works on its own. Research therefore asks about the interplay of state, society and the decisions of those involved, as the two schools above describe.
Why are most wars intrastate?
For the period between 1945 and 2020, AKUF counts 242 wars. It classifies 170 of them as intrastate, that is, about 70 percent, as Wolfgang Schreiber summed up for the Federal Agency for Civic Education in 2021.
By UCDP's definition, intrastate means that a government fights a non-state party without other countries intervening. Since 1945, war between two states has therefore not been the most common case.
One explanation is the weakness of many states, described in the section on causes. Where a state cannot contain the violence of competing actors, the framework in which disputes are settled without weapons is missing.
Which types of war does research distinguish?
AKUF distinguishes five types. Anti-regime wars are wars fought over the overthrow of those in power or over changing or preserving the political system. Autonomy and secession wars are about greater regional autonomy or breaking away from the state.
In interstate wars, the armed forces of the governments of at least two states face each other. Decolonisation wars are fought for liberation from colonial rule. In addition there is a residual category of other wars.
According to Wolfgang Schreiber, anti-regime wars account for about half of all intrastate wars worldwide, and as much as 90% in Latin America. In Asia and Europe, by contrast, secession wars dominate, with almost 60% each. In 1992 the number of intrastate wars reached a high of 53 out of 55 wars in total.
Do democracies go to war with each other?
One finding is regarded in research as relatively undisputed: the theory of the democratic peace. According to it, democracies do not go to war against other democracies.
The theory says something about wars between democracies. It does not say that democracies never wage war, and it does not explain wars within states. Ruloff and Schubiger attribute the finding less to the love of peace of democracies than to democratic control of the military and of important decisions, and to the ties created by diplomacy, trade and capital.
For the question of why, it is still revealing. It draws attention to whether the internal order of states influences how they settle conflicts with one another.
When is a war considered over?
AKUF regards a war as over when the fighting stops for good, that is, for at least one year. It is also considered over when the fighting only continues below its definition of war.
AKUF then calls such confrontations armed conflicts. The end of a war in the statistics therefore does not mean that there is no more violence.
How a war that has ended turns into a lasting peace is a question of its own. The page on making peace describes where civil conflict transformation comes in, and W3ltfrieden connects people who want to get involved with peace missions in their area.
What consequences does war have for people?
The most immediate consequence is death and injury. According to an estimate by the Uppsala Conflict Data Program, nearly 160,000 people died from organised violence in 2024.
War also forces many people to flee. According to figures from the UN Refugee Agency UNHCR, reported by the Federal Agency for Civic Education, 122.6 million people worldwide were forcibly displaced at the end of 2023, twice as many as in 2015. 63.3 million of them were internally displaced, that is, displaced within their own country. The figure covers all reasons for flight and displacement, not only wars.
The consequences reach far beyond the end of a war. As HanisauLand puts it, people often still suffer from the consequences of a war long after it is over.
Ruloff and Schubiger, Aus Politik und Zeitgeschichte, 2007, on the systemic approach, translated
From this point of view, wars are the by-product of social, economic and political upheaval.
Sources
- AKUF, University of Hamburg: definition of war, in German
- Uppsala University: UCDP Definitions
- HIIK: methodology, in German
- bpb: intrastate wars since 1945 (Wolfgang Schreiber), in German
- bpb, APuZ: armed conflicts, an overview, in German
- bpb: fragile statehood as a cause of conflict (Daniel Lambach), in German
- bpb: resource conflicts, in German
- Uppsala University: UCDP, sharp increase in conflicts and wars, 2025
- bpb: refugees, asylum seekers and internally displaced persons, in German
- HanisauLand (bpb): war, in German
- United Nations: UN Charter, chapter I
- Clausewitz Society: Carl von Clausewitz, Vom Kriege (PDF), in German
- Federal Foreign Office: guidelines on crisis prevention, in German
The five HIIK levels of intensity
- Disputelevel 1, non-violent conflict
- Non-violent crisislevel 2, non-violent conflict
- Violent crisislevel 3, violent conflict
- Limited warlevel 4, violent conflict
- Warlevel 5, violent conflict
Frequently asked questions about the causes of war
Why is there war, explained simply for children?
HanisauLand, the children's website of the Federal Agency for Civic Education, explains it like this: war can break out when the governments and politicians of different countries stop talking to each other to settle their conflicts peacefully. These states then try to settle the dispute by force, with weapons and the military.
It adds: when war breaks out, there are always many injured and dead, and people often suffer from the consequences long after the war is over.
What did Clausewitz mean by a continuation of politics?
Carl von Clausewitz wrote in his work On War: war is merely the continuation of politics by other means. It is, he wrote, not merely a political act but a true political instrument.
The sentence describes how war is connected to political aims. It is not a justification: under Article 2 of the Charter of the United Nations, all members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state.
How can war be prevented?
In its guidelines on crisis prevention, the German government commits itself to the priority of civilian means. According to the Federal Foreign Office, the aim is to recognise and defuse conflicts before they escalate. Civilian instruments such as mediation, dealing with the past or security sector reform are meant to help prevent and settle crises or avoid relapses.
Research on the democratic peace adds another thought: democracies do not go to war against each other, which according to Ruloff and Schubiger has less to do with a love of peace than with democratic control of the military and the ties created by diplomacy and trade. The page on making peace describes how peace comes about on a small scale.
Why do some wars last so long?
According to the Federal Agency for Civic Education dossier on resource conflicts, one reason lies in disputes over raw materials. Greed rarely triggers open conflicts, it says, but contributes considerably to prolonging them and preventing a peaceful solution.
The dossier also describes a so-called resource curse, observed mostly in resource-rich developing or emerging countries. Here too, raw materials alone rarely trigger a conflict; they act together with other causes.
How many people die from organised violence?
The Uppsala Conflict Data Program estimates that nearly 160,000 people died from organised violence in 2024, slightly fewer than the year before. At the same time it counted 61 active conflicts involving at least one state, the highest number since statistics began in 1946. Eleven of them reached the level of war.
This page does not describe which conflicts these are. It is about the question of why wars come about.
More on peace
- Making peacePeace does not come about by itself. It is negotiated, mediated and looked after day by day, by governments as much as by people in their neighbourhood
- Toward Perpetual PeaceIn 1795 Immanuel Kant described the conditions under which states can live together without war for good, in the form of a treaty with six preparatory and three definitive articles
From the idea to a mission of your own
Peace comes about where people shape it: in a neighbourhood, a school, a club. On W3ltfrieden you will find peace missions that you can start or support.
Find your peace mission