USMCA resulted from renegotiations between the NAFTA member states beginning in 2017; characterized as "tumultuous", these centered primarily on "auto exports, steel and aluminum tariffs, and the dairy, egg, and poultry markets". All sides came to an informal agreement on September 30, 2018, which was formalized the following October 1. U.S. President Donald Trump proposed USMCA during the 2018 G20 Summit, where it was signed by Trump, Mexican President Enrique Peña Nieto, and Canadian Prime Minister Justin Trudeau. A revised version reflecting additional consultations was signed December 10, 2019 and ratified by all three countries, with Canada being the last to ratify on March 13, 2020. Following notification by all three governments that the provisions were ready for domestic implementation, the agreement came into effect on July 1, 2020.