The Women's Loyal National League, also known as the Woman's National Loyal League and other variations of that name, was formed on May 14, 1863, to campaign for an amendment to the U.S. Constitution that would abolish slavery. It was organized by Elizabeth Cady Stanton, its president, and Susan B. Anthony, its secretary. In the largest petition drive in the nation's history up to that time, the League collected nearly 400,000 signatures on petitions to abolish slavery and presented them to Congress. Its petition drive significantly assisted the passage of the Thirteenth Amendment, which ended slavery in the U.S. The League disbanded in August 1864 after it became clear that the amendment would be approved.
The League was the first national women's political organization in the United States. It marked a continuation of the shift of women's activism from moral suasion to political action, and from a women's movement that was loosely structured to one that was more formally organized. It also contributed to the development of a new generation of leaders and activists for the women's movement.