It is hard to say for sure which battles were the most important in the history of humankind, but the world may certainly have looked a lot different if certain battles were not fought and won by the right people…
Battle of Marathon, 490 BC
The Battle of Marathon was a turning point for the Greeks, who proved to themselves that they could beat the Persians. The Classical Greek civilization rose in the 200 years that followed, which shaped western society as we know it.
Although Yorktown was not a major battle when you look at the numbers, Gen. Washington's defeat of the British army was the first step to American independence. This battle caused the British to surrender, ended the American Revolutionary War and changed the future of the U.S.A and the world.
The Battle of Waterloo stopped Napoleon in his tracks. It ended his rule as the French Emperor and forced him back into exile. If this battle didn't happen, who knows what France and Europe might have looked like today.
Invasion of Normandy, 1944
The Allied forces' invasion of Normandy on D-day was a major turning point that led to the decline of the Nazi's hold on the Western front.
The Battle of Stalingrad, 1943
When the Russians defeated the Germans in Stalingrad, it didn't only took a large chunk out of Hitler's army where numbers were concerned, but it also discouraged the Germans of trying to expand on the Eastern front.