The Lost Cause didn’t just come out of nowhere as a fully fledged ideology. It was built over time.
Right after the war, many Southerners felt the need to explain why they seceeded. One of the first books on this subject was “The Lost Cause” by Edward Pollard. After Robert E. Lee died, his eulogy also pushed the lost cause narrative.
Still, by the 1870s, it was not that strong of an ideology.
It gradually became more accepted as confederates met up at reunions and wrote memoirs that emphasized service and patriotism.
The ex-president of the Confederacy, Jefferson Davis, went on a speaking tour and wrote his own history of the Confederacy which promoted the lost cause.
In 1889, the United Confederate Veterans group was formed, and as soldiers started dying, other groups like Sons of Confederate Veterans and the United Daughters of the Confederacy were formed. The United Daughters of the Confederacy in particular played a huge role in sponsoring confederate statues, picnics, and various events to promote the lost cause.
For the most part, this was a Southern thing, but when the US declared war on Spain in 1898, there was a real need to unify the nation, so the president chose an ex-confederate soldier as the leader of the cavalry.
The Lost Cause allowed historians to explain away how a nation once divided could unify again. Ultimately, the Lost Cause was legitimized by historians. At this point in time, the US history profession was a new concept.
The first history PhD in the US was only earned in 1882, and the American Historical Association was founded in 1884. History was considered a nation building project, and the Lost Cause got wrapped up in that.
“But when American history comes to be rightly viewed it will be seen that the slavery question is an incident. In the period from the end of the first half of the present century to the close of the Civil War slavery rose to primary, but far from exclusive, importance.” - Frederick Jackson Turner (source)
William Archibald Dunning was the American Historical Association president in 1913, and he was a supporter of the South. He wrote history from a Southern perspective, and lent legitimacy to disenfranchisement. It could be argued that his work was an integral part in creating Jim Crow laws.
The ultimate legitimizer of the lost cause was President Woodrow Wilson.
“The white men were roused by a mere instinct of self-preservation...until at last there had sprung into existence a great Ku Klux Klan, a veritable empire of the South, to protect the Southern country.” - Woodrow Wilson (source)
Wilson legitimately believed that the Ku Klux Klan had saved the south from a a slave uprising. A friend of his wrote a book that later became a movie called “The Birth of a Nation”. This movie solidified what the lost cause was, and was super popular, in part thanks to Wilson screening it in the white house.
As a result of this, KKK membership skyrocketed, there was an explosion in confederate monument building and events, there was an influx in lynching, and the creation of more laws that disenfranchised black people.
This was the lowest point of American race relations.