Aphrodite, Athena, and Hera were arguing about who deserved the apple that said "the fairest of them all" on it. They decided to go to Prince Paris and have him pick who to give the apple to. He couldn't pick one because he thought they were very beautiful, so they each offered to give him something if he picked them. Aphrodite offered him the love of the most beautiful woman on Earth, so he chose her.
Queen Helen of Sparta was the most beautiful woman in Prince Paris's eyes, but she was married to king Menelaus. However, with the offer that Aphrodite had given Prince Paris, she would instantly fall in love with him. When Prince Paris visited her castle, she snuck outside with him while her husband was sleeping and went back to Troy with Prince Paris.
King Menelaus noticed that Helen was gone and thought that she was taken against her will. Menelaus's brother, Agamemnon got all of the kings together and declared war on Troy, saying that Troy needed to return Queen Helen.
After 10 long years of battle, Odysseus had an idea that would surely cause them to win the war. They were going to build a big wooden horse, and Sinon, who was a great liar, would stay as a prisoner and convince the king of Troy to allow the horse into the city walls. Men from the army would be hiding inside the horses belly and sneak out when people least expected it.
When they found the horse in front of there city walls, people were unsure about it, so they brought out Sinon and asked him about it. He was able to convince the king that it was an offering to the gods to show that they were sorry for all of the destruction they caused, so that they would have safe travels on their way home. The Trojan people believed him and let the horse in their city walls.
Everyone partied around the horse and sang holy songs. That night, the greek soldiers slipped out of the giant horse and burnt down the city of Troy. Everybody there was either too tired or dizzy to fight, so they were defenseless. Queen Helen threw herself at Menelaus's feet and said that she was taken against her will. The greeks had won the war.