The Empire of Japan aimed to dominate Asia
and the Pacific and was already at war with the
Republic of China in 1 937,[5] but the world war
is generally said to have begun on 1 September
1 939[6] with the invasion of Poland by Nazi
Germany and subsequent declarations of war
on Germany by France and the United
Kingdom. From late 1 939 to early 1 941 , in a
series of campaigns and treaties, Germany
conquered or controlled much of continental
Europe, and formed the Axis alliance with Italy
and Japan. Under the Molotov–Ribbentrop Pact
of August 1 939, Germany and the Soviet Union
partitioned and annexed territories of their
European neighbours, Poland, Finland,
Romania and the Baltic states. The war
continued primarily between the European Axis
powers and the coalition of the United Kingdom
and the British Commonwealth, with campaigns
including the North Africa and East Africa
campaigns, the aerial Battle of Britain, the Blitz
bombing campaign, and the Balkan Campaign,
as well as the long-running Battle of the Atlantic.
On 22 June 1 941 , the European Axis powers
launched an invasion of the Soviet Union,
opening the largest land theatre of war in
history, which trapped the major part of the Axis
military forces into a war of attrition. In December 1 941 , Japan attacked the United States and European
colonies in the Pacific Ocean, and quickly conquered much of the Western Pacific.
The Axis advance halted in 1 942 when Japan lost the critical Battle of Midway, and Germany and Italy
were defeated in North Africa and then, decisively, at Stalingrad in the Soviet Union. In 1 943, with a
series of German defeats on the Eastern Front, the Allied invasion of Sicily and the Allied invasion of Italy
which brought about Italian surrender, and Allied victories in the Pacific, the Axis lost the initiative and
undertook strategic retreat on all fronts. In 1 944, the Western Allies invaded German-occupied France,