The SPU was founded by Ken Calkins, who had gained notoriety when his pelvis was fractured when he sat in front of a truck during a pacifist demonstration against nuclear weapons at the first Atlas Missile site 20 miles northwest of Cheyenne, Wyoming.
[1] From the beginning, the Young People's Socialist League, then under the influence of the Shachtmanites, poured its members into the group and tried to give it a "Third camp" direction—rejecting both Western capitalism and Soviet communism as equally imperialist.
To their surprise President Kennedy displayed some sympathy for the group, having his disarmament advisers confer with picket leaders and receiving their petitions.
During the Cuban Missile Crisis that October, the group sponsored demonstrations across the country, including a march in front of the White House that drew 2,000 people.
Debates among the YPSLs over when, if ever, to support peace candidates and questions over foreign policy consumed the top leadership, and the organization dissolved in the spring of 1964.