Hippolyta, I wooed thee with my sword
And won thy love, doing thee injuries,
But I will wed thee in another key,
With pomp, with triumph, and with reveling. (1.1.17-20)
It turns out that Theseus and Hippolyta are getting hitched because Theseus conquered Hippolyta's people, the Amazons. As we know, the Elizabethans were fascinated by classical myths about Amazons, women who cut or burned off their breasts so they could shoot a bow and arrow more efficiently, raised their daughters to be warriors, dominated their husbands, and treated their sons badly by sending them away, making them do "girlie" housework, and/or by killing them.
Why does this matter? Well, because Amazons dominate men, they flip the traditional European gender system on its head. In Shakespeare's play, though, men regain their positions of power over women. (Theseus marries the Amazonian Queen he won in battle and, also, Oberon humiliates Titania and takes away her foster child). At least that's how literary critic Adrian Montrose sees it. He argues that A Midsummer Night's Dream "eventually restores the inverted Amazonian system of gender and nurture to a patriarchal norm."
Brain Snack: In one of Shakespeare's major sources (Plutarch's "The Life of Theseus"), Theseus easily beats the Amazons in battle and captures Hippolyta after luring her onto his boat. (According to Plutarch, Theseus is the McLovin of the ancient world, so Hippolyta could hardly resist his charms.) You can read the story here.