Shakespeare may have used Homer's account of the Trojan War as a major literary source, but warfare in Troilus and Cressida is far from epic or heroic. Seven years into the war, the Greek camp is in total chaos and the deeds performed on the battlefield are gruesome, dishonorable, and shameful. (Just ask Achilles, who kills an unarmed soldier and then has his body dragged around the fields by his horse.) If the actions that go down on the battlefield of Troy are bad, the cause of the Trojan War is even worse. We're reminded over and over again that the Trojans and the Greeks are fighting because Paris stole Helen from the Greek King Menelaus. And even though the Trojans insist they fight to keep Helen as a matter of "honor," the play crudely states that that "all the argument is a cuckold and a / whore" (2.3.71-72). In other words, the conflict that costs countless lives, money, and time is being fought because of a torrid sexual relationship. Pretty ridiculous, wouldn't you say?
Troilus and Cressida reduces the entire Trojan War to a conflict caused by a steamy sexual hook-up.
Helen isn't the actual cause of the conflict in this play—she's just an excuse for the Greeks and Trojans to wage war and earn props from other men on the battlefield.