Answer: Geographical proximity, Economic growth in the USA and new immigration laws.
Explanation:
For Mexico, the geographical proximity to the new giant put a density of economic, social and political relations unparalleled in the rest of Latin America. Nevertheless, as soon as the United States entered the war, the ties were further tightened. Concerned about the neighbor's position in the face of the conflict, the United States was prepared to stop the wounds caused by the oil issue and the expropriation enacted in 1938. They pledged to provide technical and financial assistance for activities that could be useful to their economy of war and post war. Besides that, President Johnson signed the Immigration and Nationality Services Act of 1965 that treated all nationalities and raced equally. The new act allowed the entry of immediate family members of American residents without limit. During the sixties, Asians and Latin Americans became the largest contingent of new Americans.