What were the causes of the World Wars?

In the First World War the European hegemony over the world had reached its peak and 1st World War was really about Europe. Because European countries had colonies it spread over the world.

The Diplomatic system of European Alliances had reached the end of its ability to effective manage conflict between the empires. The Empires were starting to be unable to continue to govern their peoples.

Technology had a lot to do with this. Large and powerful conscription based armies convinced Empires that they could overwhelm their enemies. Communications technology sped things up. Transportation Technology moved larger armies and more supplies faster.

Nationalism both supported and eroded the empires. The Nationalism of minorities pulled the empires apart and the Nationalism of the majority pitted it against the foreigner.

Brinkmanship and the the Diplomatic system of Alliances was not quick enough or powerful enough to stop the war from starting. Once the War started nothing could stop it and it destroyed many of the empires that existed in the beginning.

Only the threat of immediate defeat forced the German General Staff to sue for peace.

The Peace brokered at the end of World War 1 led in many ways to World War 2. The crushing burden of reparations and other aspects of the settlement was more than the moderate German Government could deal with and it was overwhelmed by opportunistic extremists.

World War 1 had helped to create the Soviet Union. Its anti-capitalist ideology stifled communication with the West which helped the situation get out of hand.

Asian Nationalism was fostered in the interwar period. Japan wanted to be a Great Empire as well. They were snubbed by the West and it bred resentment.

The League of Nations failed and Peace through disarmament failed in the face of ambitious ideological extremists.

New and more powerful technologies made a more complex, faster, more powerful and destructive armies. Nuclear weapons were an ultimate goal.