Aphrodite the goddess of love and beauty promised for Helen to marry Paris. However she was married to Menelaus younger brother of King Agamemnon of Micenae, for the goddess to win a proposition.
This is how the war started after Helen fell in love with Paris, Agamemnon the King was furious and declared war which eventually went on for a decade.
After 10 years, the Trojans then believed that they had won the war received the forfeit from the Greeks of a wooden horse. Little did they know there were warriors hiding inside who eventually crept out at the night unlocked the big gate, and attacked the Trojans winning the war.