The Trojan War in a war in the Greek Mythology fought between the Greeks and the people of Troy. It began when the prince of Troy, Paris, kidnapped Helen, the wife of Menelaus (lord of Sparta). The Trojans refused to return her to her husband. So, Menelaus along with his brother began the war against Troy.
because paris the prince of troy eloped helen
According to Greek mythology Paris the prince of Troy stole the wife of Menelaus the king of Sparta .The king took the support of great king Ulysses and Achilles the  son of god Thesis. And after long voyage in the sea they reached the city of Troy and destroyed the city and and took her back to the Sparta.