SAN DIEGO (AP) – A new study finds more Mexicans leaving the United States than coming into the country.

That marks a reversal to one of the most significant immigration trends in U.S. history.

The Pew Research Center has found that slightly more than 1 million Mexicans and their families left the U.S. for Mexico from 2009 to 2014. During that same five years, 870,000 Mexicans came to the U.S., resulting in a net flow to Mexico of 140,000.

Pew said Thursday that a desire to reunite families is the primary reason Mexicans go home, along with the sluggish U.S. recovery from the Great Recession.

Meanwhile, tougher border enforcement has reduced the number of Mexicans coming into the United States.