After the war, Confederate states were readmitted to the Union during the Reconstruction era, after each ratified the 13th Amendment to the U.S. Constitution, which outlawed slavery. "Lost Cause" ideology—an idealized view of the Confederacy as valiantly fighting for a just cause—emerged in the decades after the war among former Confederate generals and politicians, as well as organizations such as the United Daughters of the Confederacy and the Sons of Confederate Veterans. Particularly intense periods of Lost Cause activity came around the time of World War I, as the last Confederate veterans began to die and a push was made to preserve their memory, and then during the Civil Rights Movement of the 1950s and 1960s, in reaction to growing public support for racial equality. Through activities such as building prominent Confederate monuments and writing school history textbooks to paint the Confederacy in a favorable light, Lost Cause advocates sought to ensure future generations of Southern whites would continue to support white supremacist policies such as the Jim Crow laws. The modern display of Confederate flags primarily started during the 1948 presidential election when the battle flag was used by the Dixiecrats in opposition to the Civil Rights Movement and has continued to the present day.