President-elect Donald J. Trump announced plans to impose a 25 percent tariff on all goods entering the United States from Canada and Mexico. He stated these tariffs would remain in place until the flow of drugs and unauthorized migrants across the U.S. borders was stopped.

Mr. Trump specifically highlighted a group of migrants traveling north from southern Mexico as part of a caravan. He has frequently used such migrant caravans to emphasize his concerns about border security, despite the fact that they rarely reach the United States.

These large groups of migrants often gather in southern Mexico near the border with Guatemala, more than 1,000 miles away from the United States. Their primary motivation for traveling together is the safety and security provided by numbers.

Many migrants wait in the southern Mexican city of Tapachula for humanitarian visas, which can take months to process. During this time, they join forces to prepare for their journey northward. The trip across Mexico is fraught with dangers, especially for those with limited resources, as they face threats of kidnapping, extortion, and violence from criminal gangs or corrupt officials. Traveling in a caravan helps mitigate these risks and provides an alternative to the costly services of smugglers.

Migrants from across the Americas—and increasingly from regions like Asia and Africa—make their way to southern Mexico, often enduring long, perilous journeys through jungles and multiple borders. However, the caravans they form are rarely able to reach the U.S. border intact. Mexican authorities frequently break them up well before they get close, either due to the physical toll of the journey or negotiations between officials and migrants, who sometimes disperse after receiving promises of temporary travel permits.

The Mexican government has implemented various measures to discourage migrants from heading north, including transporting them to southern regions of the country, far from the U.S. border.

Recently, a caravan of about 1,500 people, primarily from Central and South America, was reported by the Associated Press to have formed in southern Mexico. This group aims to reach the United States before Mr. Trump’s inauguration in January.