Battle of Stalingrad (17 jul 1942 año – 2 feb 1943 año)

Descripción:

Who - The Soviet Union, Nazi Germany, Italy, Croatia, Romania, and Hungary
What - Germany and its allies fought the Soviet Union
Where - Stalingrad, Russia
Why - Germany wanted oil from Stalingrad

The Battle of Stalingrad helped stop Nazi Germany from invading more of Europe and/or Russia. This was one of the first major losses on Germany's side of things.