High Quality Content by WIKIPEDIA articles! Negative Population Growth is a membership organization in the United States, founded in 1972.NPG works on overpopulation issues and advocates a gradual reduction in U.S. and world population. NPG believes the optimal population for the United States is 150 to 200 million and that the optimal world population is two to three billion. In order to accomplish their goal of a smaller U.S. population, the organization promotes policies which would reduce the fertility rate in the U.S. to 1.5 births per woman, and they advocate for reducing the level of immigration into the United States to 100,000 to 200,000 per year from the existing level of over 1.5 million per year.