When many Central Americans began appearing at the U.S.-Mexico border in 2013 and 2014, Americans reacted with surprise. Why were Central Americans suddenly deciding to come to the United States now? Of course, there is more than one answer, but perhaps the most important missing context is that just as many Central Americans were trying to reach the United States in earlier years. They just didn’t make it.

Figure 1 shows the number of arrests of Central Americans from the Northern Triangle by Mexican authorities and by the U.S. Border Patrol from 2001 to 2019. As it shows, arrests in 2005 and 2006 rivaled those from 2014 to 2018, but the large majority of the arrests were made in Mexico, not the United States. U.S. and Mexico apprehensions declined together from 2001 to 2011, but starting in 2012, they increased much faster in the United States than in Mexico, meaning far more Central Americans made it to the U.S. border.

In 2006, just 30 percent of Central Americans arrested made it to the United States, while 70 percent were arrested in Mexico. By 2014, these percentages had flipped, even though total arrests in both countries were nearly the same. Mexico temporarily ramped up enforcement and had a majority of the arrests in 2015 but by 2019, the percentages reached another record high. The increase in migrants reaching the United States first coincided with an absolute increase in migration from 2001 to 2006, but it continued to increase from 2007 to 2011 even with a large decrease in total arrests.

Figure 2 provides the share of U.S. and Mexican arrests of migrants that were made in the United States by migrant country of origin. As it shows, Guatemala has seen the largest increase in the share of arrests made in the United States. In 2001, Guatemalans were the most likely to be arrested in Mexico. By 2019, they were the least likely. In most years, however, Salvadorans were the least likely among the Northern Triangle countries to be arrested in Mexico. Interestingly, migrants from the rest of the world—mainly India and South America—started out most likely but by 2019 were least likely to reach U.S. soil.

Figure 3 presents a more limited time series—from 2007 to 2019—of the number of arrests of children and adults, with a breakdown by status for 2014 to 2019. It indicates that families and children are much more likely to reach the United States than single adults in almost every year. Interestingly, the likelihood of children being arrested in the United States increased from 2008 to 2010, while little change occurred for adults until 2012. After that point, adults, parents, and children move in tandem. The rise of child and family migration could explain at least part of the decrease in the effectiveness of Mexican enforcement, though why children more easily escape notice than adults is unclear.

Monthly data can help identify more precisely when these changes occurred. Unfortunately, the data are not as complete. Figure 4 presents the available data—mostly for children and families. It appears that something may have occurred in late 2009 that reduced the effectiveness of enforcement in Mexico against children, and then again in mid- to late-2012. It certainly looks like Mexico’s crackdown in 2019 had a greater effect on single adults than families and children. This is surprising because the absolute number of families declined much faster in June and July than single adults did.

Mexican immigration has proved less effective at stopping Central Americans from reaching the United States, and prior to 2019, this was the primary reason for unprecedented Central American arrests by U.S. Border Patrol. More than other nationalities, Guatemalans saw the biggest increase in the share of arrests happening in the United States. Mexico has had more difficulty controlling the flow of children and families, and the increase in those types of migrants explains at least part of the change.

Over this period, Mexican immigration policy shifted in a more humane direction, culminating in a sweeping reform in 2012. Mexico both issued more visas and provided more effective controls on immigration agents. These actions may have made it easier for migrants to avoid being stopped in Mexico and reach the U.S. The simultaneous disappearance of Mexican illegal immigration and bulk marijuana trafficking may have also caused smuggling organizations to focus their efforts on moving Central American migrants, making the migrants more effective. Whatever the case, the ability of Central Americans to reach the U.S. border has been the most important change in Central American migration—not their willingness to try.