Before the Columbian exchange, there was an open border policy in the Americas that gave Native Americans access to travel freely and have open trade with other cultures. There was widespread trade among many First Nations that created free movement and travel for many foreigners. At the time, there was little border control which allowed migrants to travel to various areas to settle. Immigration policy shifted towards control and nationalism after 1492. In the 20th century, immigration policy solidified borders in America, but many Native Americans advocated free movement and hospitality towards strangers. Native Americans historically have welcomed strangers with hospitality, sometimes making them relatives through an informal adoption system. Migration in America can be understood through the religious and cultural perspectives of Native Americans.