Complex sentence: The Commission for Environmental Cooperation was created in 1994 by Canada, Mexico and the United States under the North American Agreement on Environmental Cooperation, a treaty implemented in parallel to the North American Free Trade Agreement (NAFTA) to complement the environmental provisions of NAFTA.
Split into simpler sentences: The Commission for Environmental Cooperation was created in 1994 by Canada, Mexico and the United States, under the NAAEC. The NAAEC was implemented in parallel to the North American Free Trade Agreement (NAFTA), and complements the environmental provisions of NAFTA.