One significant period in war history is World War II, which lasted from 1939 to 1945 and involved most of the world's nations. It began with the invasion of Poland by Germany and quickly escalated as other countries, such as the United Kingdom, France, and the Soviet Union, became involved.

The conflict resulted in an estimated 70-85 million fatalities including civilians and military personnel. The use of new technologies like tanks, aircrafts, and atomic bombs dramatically changed warfare tactics.

World War II ended with Allied victory over Axis powers but left a lasting impact on global politics and society. Its legacy includes major geopolitical shifts including the division of Europe during the Cold War era between the US-led Western Bloc against the Soviet-controlled Eastern Bloc.