Immigration and migration have always been part of the American story. One of our foundational myths is that the United States is a land of boundless opportunity—there for the taking by the industrious and the brave. And for the better part of two centuries, immigrants and migrants took this myth to heart and followed its pull westward.

In his seminal 1893 essay, “The Significance of the Frontier in American History,” Frederick Jackson Turner proposed a “frontier thesis,” which suggested that American democracy—American culture, really—was forged on the ever-moving western frontier.