Few Thais immigrated to the United States prior to 1961, and there was virtually no Thai food served in restaurants in the United States up to that time. The Vietnam War changed this. The U.S. Air Force had a sizable presence in Thailand during the war and many servicemen returned home with a taste for Thai food. Thai immigration to the United States increased for a number of reasons including: marriage to American military personnel, nurses recruited from Thailand during a U.S. shortage, and a liberalization of U.S. immigration policy toward Asians. Thais have continued to migrate to the United States due to political unrest in Thailand and economic opportunities here.