We already know that federal housing policies such as redlining, real estate practices like blockbusting, and the resulting “white flight” to suburbs in post-World War America caused cities to segregate, sealing generations of African Americans into poverty.

But even if these discriminatory policies hadn’t existed, the fate of our cities may not have been all that different, a new working paper published in the National Bureau of Economic Research suggests.

Economists Allison Shertzer and Randall P. Walsh at the University of Pittsburgh analyzed data from 10 large U.S. cities in the Northeast and the Midwest from 1900 to 1930 to isolate the role of white flight that occurred in that period—before the Federal Housing Authority, which instituted many of the discriminatory housing policies, was born. They found that the exodus of white people from a particular neighborhood following the arrival of black residents led to a 34 percent increase in segregation during the 1910s; In the 1920s, it resulted in a striking 50 percent increase.

Here’s how the authors summarize their findings in the NBER paper:

Our finding that sorting by whites out of neighborhoods with growing black population was a quantitatively important phenomenon decades before the postwar opening of the suburbs is novel. This analysis suggests that segregation would likely have arisen even without the presence of discriminatory institutions as a direct consequence of the widespread and decentralized relocation decisions of white individuals. Whites could simply have responded to policies that reduced barriers to black settlement in their vicinity by accelerating their departure for neighborhoods at lower risk of “encroachment.”