"The heavy immigration from Mexico was a consequence of economic problems in that country, as well as a result of opportunities and relatively liberal immigration policies in the United States. More than 70 percent of Mexico’s export revenues came from oil at the beginning of the 1980’s. As the price of oil declined beginning about 1982, Mexico had less revenue coming in, provoking a debt crisis, and the country’s already existing problems of poverty became worse. Legal immigration from Mexico began to move upward rapidly, from a little over 621,000 in the decade 1970-1979 to over one million during the 1980’s. The Immigration Reform and Control Act of 1986 encouraged some undocumented Mexicans in the United States to remain by offering amnesty, and it encouraged others to move into the United States on a long-term basis by intensifying control of the border, making it more difficult to move back and forth. The longer-term orientation led many workers to move further north, away from the border. In 1994, a second economic shock hit Mexico, with the devaluation of the peso, which caused dramatic inflation and a decline in living standards. In response to the economic problems, legal migration grew even more during the 1990’s, with more than 2.75 million Mexicans entering the United States. From 2000 to 2005, the United States received an average of 200,000 legal permanent residents from Mexico every year."