Mates of Helen
The legendary beauty of Helen attracted men from afar and also those close to home who saw her as a means to the Spartan throne. The first likely mate of Helen was Theseus, hero of Athens, who kidnapped Helen when she was still young. Later Menelaus, brother of the Mycenaean King Agamemnon, married Helen. Agamemnon and Menelaus were sons of King Atreus of Mycenae, and were therefore referred to as Atrides. Agamemnon married the sister of Helen, Clytemnestra, and became king of Mycenae after expelling his uncle. In this way, Menelaus and Agamemnon were not only brothers but brothers-in-law, just as Helen and Clytemnestra were not only sisters, but sisters-in-law.
Paris and Helen
Paris (aka Alexander or Alexandros) was the son of King Priam of Troy and his queen, Hecuba, but he was rejected at birth, and raised as a shepherd on Mt. Ida. While living the life of a shepherd, the three goddesses, Hera, Aphrodite, and Athena, appeared to him asking him to award the "fairest" of them the golden apple that Discord had promised one of them. Each goddess offered Paris a bribe, but the bribe offered by Aphrodite appealed to Paris most, so Paris awarded the apple to Aphrodite. It was a beauty contest, so it was appropriate that the goddess of love and beauty, Aphrodite, had offered Paris the most beautiful woman on earth for his bride. This woman was Helen. Unfortunately, Helen was taken. She was the bride of Menelaus.
Paris Kidnaps Helen
Whether or not there was love between Menelaus and Helen is unclear. In the end, they may have been reconciled, but meanwhile, when Paris came to the Spartan court of Menelaus as a guest, he may have aroused unaccustomed desire in Helen, since in the Iliad, Helen takes some responsibility for her abduction. Menelaus received and extended hospitality to Paris. Then, when Menelaus discovered that Paris had taken off for Troy with Helen and other prized possessions Helen may have considered part of her dowry, he was enraged at this violation of the laws of hospitality. Paris offered to return the stolen possessions in the course of the Iliad, even when he is unwilling to return Helen, but Menelaus wanted Helen, too.
Agamemnon Marshalls the Troops
Before Menelaus won out in the bid for Helen, all the leading princes and unmarried kings of Greece had sought to marry Helen. Before Menelaus married Helen, he (actually, Helen's earthly father) extracted an oath from these, the Achaean leaders, that should anyone try to kidnap Helen again, they would all bring their troops to win back Helen for her rightful husband. When Paris took Helen to Troy, Agamemnon gathered together these Achaean leaders and made them honor their promise. Agamemnon then led the troops to Aulis -- the point from which they would sail to Troy -- where there was a delay.