After diplomatic negotiations in 1990, the heads of state and government of the three nations signed the agreement on 17 December 1992 in their respective capitals.  The signed agreement had to be ratified by each country`s legislative or parliamentary department. The OBJECTIVE of NAFTA was to remove barriers to trade and investment between the United States, Canada and Mexico. The implementation of NAFTA on January 1, 1994 resulted in the immediate removal of tariffs on more than half of Mexican exports to the United States and more than one-third of U.S. exports to Mexico. Within 10 years of the implementation of the agreement, all U.S.-Mexico tariffs should be eliminated, with the exception of some U.S. agricultural exports to Mexico, which are expected to expire within 15 years.  Most of the trade between the United States and Canada was already duty-free. NAFTA also aimed to remove non-tariff barriers and protect intellectual property rights on marketed products. Additional ancillary agreements have been adopted to allay concerns about the potential impact of the treaty on the labour market and the environment. Critics feared that U.S.
and Canadian companies in Mexico would have generally low wages, which would lead to a shift of production to Mexico and a rapid reduction in manufacturing employment in the United States and Canada. Meanwhile, environmentalists were concerned about the potentially catastrophic effects of rapid industrialization in Mexico, which does not have experience in implementing and enforcing environmental legislation. Possible environmental problems were raised in the North American Environmental Cooperation Agreement (NAAEC), which established the Commission for Environmental Cooperation (CEC) in 1994. Economists generally agreed that the U.S. economy as a whole benefited from NAFTA by increasing trade.   In a 2012 survey by the Global Markets Initiative`s panel of economic experts, 95% of participants said that U.S. citizens benefited on average from NAFTA, while no one said that NAFTA was detrimental to U.S. citizens on average.  A review of the 2001 Journal of Economic Perspectives showed that NAFTA was a net benefit to the United States.  A 2015 study showed that welfare in the United States increased by 0.08% and intra-block trade in the United States by 41% due to NAFTA tariff reductions.  In July 2017, the Trump administration presented a detailed list of changes it wanted to make to NAFTA.  The top priority was to reduce the U.S.
trade deficit.   The government has also called for the abolition of provisions allowing Canada and Mexico to challenge U.S. tariffs and impose import restrictions on the United States, Canada and Mexico.  The list also highlighted subsidized state-owned enterprises and monetary manipulation.   President Donald Trump courted by promising to end NAFTA and other trade agreements he considered unfair to the United States. On August 27, 2018, he announced a new trade agreement with Mexico, which is expected to replace it. The U.S.-Mexico trade agreement, as has been said, would maintain duty-free access for agricultural products on both sides of the border and eliminate non-tariff barriers, while encouraging more agricultural trade between Mexico and the United States and effectively replacing NAFTA.