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 his leaving North Africa permanently the following
year.

Stalingrad was perhaps the most significant of these
three battles in terms of its affect on the war's outcome.  This battle was massive in
terms of the size of the German and Soviet Armies involved, the amount of material
needed, and the obscene losses suffered by both sides.  After five months of frozen,
bloody hell, the entire German Sixth Army under Field Marshall Friedrich Von Paulus
surrendered.  115,000 German soldiers were marched off to Soviet POW camps.  Only 5000
ever returned home to Germany, and it was the last major offensive they could make on
the Eastern Front.