The system approach allows to analyze the impact of cause-and-effect relationships in the migration processes development. From this position, the changes taking place in the migration processes on different sides of the Mexican-American border are considered. In the Republican President D. Trump rhetoric, the Southwest border line has become a kind of frontier separating the civilization from a chaos. The U.S. border Wall has gained symbolic value in internal and foreign policy. The U.S. regulatory policy reinforcement has changed the previously established subregional migration system, including the United States, Mexico and the Northern Triangle states of the Central America – Guatemala, Honduras and El Salvador. Mexico is forced to a more active transit migration resistance. At the same time, the number of refugees and asylum seekers in Mexico grows. In fact, it began to play the Safe Third Country role for the U.S. asylum seekers from Central America. However, the migration push factors continue to increase in the Central American countries, and the migration pressure will activate. All these processes lead to significant changes in the existing mobility forms in the subregional migration system.