community reaches a critical threshold, migration becomes self-perpetuating.” In the United States Different groups of immigrants have employed chain migration among the different strategies used to enter, work, and live in the various republics of the Americas throughout their history. Social networks for migration are universal and not limited to specific nations, cultures, or crises. One group of immigrants to the British colonies in North America (and later the United States) was African slaves brought over forcibly; the circumstances of their migration do not fit the criteria of chain migration of free labor. Other groups, such as Germans fleeing chaos in Europe in the mid-1800s, Irish fleeing famine in Ireland in the same years, Eastern European Jews who emigrated from the Russian and Austro-Hungarian Empires in the late 1800s and early 1900s, and Italians and Japanese escaping poverty and seeking better economic conditions in the same period, did use chain migration strategies extensively, with resulting "colonies" of immigrants from the same villages, towns, and cities settling in enclaves in such cities as Boston, New York, São Paulo, Rio de Janeiro, Buenos Aires, Toronto, Montreal, Sydney, Melbourne, Auckland and Havana from the mid-1800s through the mid-1900s. Italian immigration in the late nineteenth and early twentieth century relied on a system of both chain and return migration. Chain migration helped Italian men immigrate to such cities as New York in the United States and Buenos Aires in Argentina for work as migrant laborers. Italians generally left Italy due to dire economic conditions and returned wealthy by Italian standards after working in the Americas for a number of years. Italian immigrants were called ritorni in Italy and grouped with other Southern and Eastern European migrant laborers under the term “birds of passage” in America. However, after the passage in the United States of the Immigration Act of 1924, return migration was limited and led more Italians to become naturalized citizens. The networks that had been built up by information and money due to chain and return migration provided incentives for Italian permanent migration. Mexican migration to the United States from the 1940s to the 1990s followed some of the same patterns as Italian immigration. While immigrants to the United States from European nations during the period before the McCarran–Walter Act of 1952 were able to immigrate legally if with relative levels of ease depending on country of origin, the Chinese Exclusion Act of