Net migration has been the main driver of U.S. population growth for several decades, resulting in direct and lasting ecological effects. Calls for population stabilization were at the forefront of the U.S. environmental movement from the 1970s until the late 1990s. Multiple bipartisan federal commissions recommended that the U.S. government pursue population stabilization as a policy objective and recognized immigration as the main driver of future U.S. population growth. By the year 2000, the Sierra Club and the other major U.S. environmental groups had reversed their position and now lobby against any effective immigration restrictions. While the European Union is facing a much different demographic situation than the United States, both of their futures will be determined in large part by immigration policies.
