 However, in recent years some political parties have proposed an amendment of the Constitution in order to allow the Mexican army, air force or navy to collaborate with the United Nations in peacekeeping missions, or to provide military help to countries that officially ask for it.Since the North American Free Trade Agreement (NAFTA) went into effect on January 1, 1994, relations between Canada, Mexico and the United States have significantly strengthened politically, economically, socially and culturally.During the Fox administration, a further integration towards Mexico's northern neighbors was a top priority.