Nothing ´cause there is only 2 wars in all the World.
The Serbian assassination of the Austrian Archduke Ferdinand.
they fought
The disagreement that eventually turned into the Persian gulf war was the Iraqi invasion of Kuwait. When the Iraqi troops would not leave Kuwait, the Persian gulf war began with military force under the Reagan administration.
hitler
every body stinks u.s is awesome we kick their buts
The immediate origins of World War 1 lay in the decisions taken by statesmen and generals during the July Crisis of 1914 caused by the assassination of Archduke Franz Ferdinand and his wife Sophie by Gavrilo Princip.
The disagreement that turned ultimately into the World War 2 was the assassination of Archduke Franz Ferdinand of Austria. He and his wife were shot dead by a group of 6 Bosnian Serbs who had hoped to split the Austria-Hungarian country through the middle, East to West.
The immediate origins of the war ay in the decisions taken by statesmen and generals during the July Crisis of 1914 caused by the assassination of Archduke Franz Ferdinand and his wife Sophie by Gavrilo Princip.
World War I had its beginnings in a serious "disagreement" between rival groups within the Austro-Hungarian Empire, the dominant group and a handful of independence-minded groups which resented imperial control. When the tensions between these groups erupted into violence with the assassination of Archduke Ferdinand (a leader among the dominant group), World War I soon erupted, as well, with various nations coming to the aid of one or the other of the groups involved in the rivalry until nearly the entire world was at war.
Cold War
The submarine.
World War I wasn't the most destructive war. World War II was. World War II had over eight times as many casualties as World War I and also brought total war to a whole new level. It completely put Europe in ruins, but World War II was definitely the war to end all wars. After that came the Cold War, which was just political disagreement with words thrown around.