World War II started with the German invasion of Poland in 1939, which triggered declarations of war from France and the United Kingdom, formally beginning the war
. The conflict lasted from 1939 to 1945 and involved the vast majority of the world's countries, including all the great powers, fighting as part of two opposing military alliances: the Allies and the Axis
. The war resulted in 70–85 million fatalities and is considered the deadliest conflict in history
