Zeus, the King of the gods, had a hard time to decide, since all three were dear to him, so he left the judgement to the most handsome young man- the Trojan Prince Paris.
Hera and Athena did their best to bribe Paris with power and glory...
Aphrodite, on the other hand, seduced him with love, offering him the most beautiful woman in the world: the legendary Helen of Sparta.
Paris opted for Aphrodite and so Helen was taken away from Sparta to become Helen of Troy.
According to one version in Greek mythology, this was the inception of the legendary Trojan War, which lasted for ten years.