“I love a great love story,” Meghan Markle told an interviewer a few weeks before she and Prince Harry announced their engagement. Their wedding, months later, was watched by a global audience that ran into the hundreds of millions. “Two people fell in love and we all showed up,” read one headline. A more sweeping advertisement for the partnership between love and marriage would be hard to come by: This was the fairy tale of romantic attraction transforming, via white wedding, into marital bliss.

But love has not always been the bedrock for entering into marriage that it is across swathes of the world today. Throughout history, it has played different roles: from a happy by-product to a threat to social order. In the Hindu tradition, notes historian Stephanie Coontz, author of ...