"Since 2014, Mexico has helped the United States manage a surge in unauthorized migration from the 'northern triangle' of Central America (El Salvador, Guatemala, and Honduras). Collectively, those countries have overtaken Mexico as the primary source for migrants apprehended at the U.S.-Mexico border. From 2015 to November 2018, Mexico reported apprehending almost 524,000 migrants and asylum seekers from the northern triangle. As U.S. asylum policies have tightened, Mexico also has absorbed more Central Americans in need of humanitarian protection (see Figure 1). President Andrés Manuel López Obrador has thus far been willing to shelter some U.S.-bound Central American migrants, but he urged the U.S. government to invest in southern Mexico and Central America to prevent future unauthorized migration."
CRS In Focus, IF10215
Congressional Research Service: https://crsreports.congress.gov/