Answer:
Prior to the war, Germany had incorporated and invaded neighboring Austria and Czechoslovakia in the years 1938-39 and Japan was already at war with China from 1937 on. From late 1939 to early 1941, in a series of campaigns and agreements, Germany conquered and annexed a significant portion of continental Europe: Poland, Belgium, Denmark, France, Greece, Luxembourg, Norway, Netherlands and Yugoslavia. They also controlled the northern part of Africa and many territories in the Middle East.
In June 1941, Germany, with its allies in the Axis, initiated an invasion of the Soviet Union known as Operation Barbarossa. The attack evolved to become the largest land-based war campaign in history, tying up most of the Axis's military forces.
In December 1941, Japan, which wanted greater dominance over eastern Asia and the Pacific (it already controlled large parts of China, Korea and many Pacific islands), attacked the United States as well as European colonies and territories in the Pacific, in a swift conquest of the Western Pacific.
The Axis advance was halted in 1942, after the Axis powers lost the decisive Battle of Stalingrad and lost the initiative in North Africa, while Japan lost a number of naval battles against the United States.
