The secular movement refers to a social and political trend in the United States, beginning in the early years of the 20th century, with the founding of the American Association for the Advancement of Atheism in 1925 and the American Humanist Association in 1941, in which atheists, agnostics, secular humanists, freethinkers, and other nonreligious and nontheistic Americans have grown in both numbers and visibility. There has been a sharp increase in the number of Americans who identify as religiously unaffiliated, from under 10 percent in the 1990s to 20 percent in 2013. The trend is especially pronounced among young people, with about one in three Americans younger than 30 identifying as religiously unaffiliated, a figure that has nearly tripled since the 1990s.