Why were Midway, El Alamein, and Stalingrad important turning points in the war?

The Battle of
Midway, which resulted in the loss of four Japanese Aircraft Carriers, was the first major
defeat for the Empire of Japan, and was the farthest their forces would advance in the Pacific. 
From 1942 on, there would be campaign after campaign aimed at "island hopping" back
towards to the Japanese home islands.

At El Alamein in North Africa in 1942,
British General Berland Law Montgomery ended any last chance the German Afrika Korps under Irwin
Rommel had of taking control of Egypt and the Suez Canal.  He then had to stage a 1500 mile
retreat that ended with...