Migration has existed as long as there have been humans. Prehistoric people from Africa mixed with Neanderthals. The migration of peoples has shaped the world. The Roman Empire dissolved when Germanic tribes, Goths and Vandals immigrated en masse.
In modern times, there were refugee movements after major wars and revolutions. After World War II, Poland was shifted westward, many Poles were forcibly resettled. Many Germans fled or were expelled, came to the remaining Germany, resettled here. After Mao Tse Tung's Great March and his revolution in China, many Chinese fled to Taiwan. Since 2006, China has been forcibly resettling millions of Tibetans. After the Vietnam War, many Vietnamese fled across the China Sea, becoming proverbial boat people. Cubans fled from the socialist dictatorship to Florida and otherwise to the USA. Mexicans have been fleeing en masse to the U.S. since the 1980s. Spanish is de facto second official language in southern states from Arizona to Texas.
So migration is nothing new. Triggers and drivers of migration movements are on the one hand wars, civil wars, bloody tribal feuds, revolutions and genocide, on the other hand poverty, hunger and droughts, caused by colonial or post-colonial exploitation, corrupt regimes, climate change, industrial overexploitation of natural resources, raw materials, water from rivers and groundwater.