Prior to NAFTA, Mexican tariffs on U.S. imports were 250% higher than U.S. tariffs on Mexican imports. In 1991, Canada requested a trilateral agreement, which then led to NAFTA. In 1993, concerns about liberalization of labor and environmental regulations led to the adoption of two addendums.
NAFTA was signed by President George H.W. Bush, Mexican President Salinas, and Canadian Prime Minister Brian Mulroney in 1992. It was ratified by the legislatures of the three countries in 1993. The U.S. House of Representatives approved it by 234 to 200 on November 17, 1993. The U.S. Senate approved it by 60 to 38 on November 20, three days later.
It was finally signed into law by President Bill Clinton on December 8, 1993 and entered force January 1, 1994. Although it was signed by President Bush, it was a priority of President Clinton's, and its passage is considered one of his first successes. (Source: History.com, NAFTA Signed into Law, December 8, 1993)