The war lasted 6 years
World war 1 lasted for 4 years (1914-1918).
WWI lasted about four years, 1914-1918, generally, with the US entering the war in 1917.
World war 2
World War I
no
World War 1 lasted for 4 years (1914-1918).
Several years into the future, and long after World War III.
World War II
World War II
World War 2
after world war 2