Which countries send migrants to the U.S. border, and what are they fleeing?

Migrants cross the Rio Grande river into the United States from Ciudad Juarez, Mexico, Wednesday, March 29, 2023, a day after dozens of migrants died in a fire at a migrant detention center in Ciudad Juarez. (AP Photo/Christian Chavez)

The deadly fire at a migrant detention center in northern Mexico last week has put . . .