There are a lot of great books that dive into this topic, but one I’d recommend is Race and Reunion by David Blight. His argument is too intricate to completely lay out here, but essentially he argues that the United States actually came together as a nation in the decades following the Civil War by ignoring the racial implications of the war and instead glorifying the soldiers of both sides. This is how the ideas of the confederacy were shifted and the Lost Cause was created, which perpetuated the narratives that keep people supporting the Confederacy even to this day.

In the immediate period following the war, the South had been forced into reunion with the North, but Southerners themselves were not prepared to completely accept idealogical defeat. Federal occupation and civil rights bestowed on African Americans created friction throughout the South. It’s also important to note that both sides had felt the massive scale of death the war caused. Families across the nation wanted to do what they could to honor their lost sons, including decorating graves, a practice that eventually morphed into the creation of Memorial Day. Southern organizations were some of the first to organize this practice on a large scale, and while they acknowledged their sons died for the Confederacy, they did not consider them traitors to American ideals. Through a shared process of national mourning that coincided with a rise in interest in war stories, the North and South began the process of reconciliation, not just reunion. Lasting throughout the rest of the 1800s, the national idea of what the Civil War meant began to shift, the role of honorable soldiers fighting for what the believed in taking center stage while the racial implications of the war vanished.

By the late 1800s and early 1900s, the Lost Cause ideology (born from the rebranding of Confederate dead through Memorial Day) had largely taken root. The South no longer seceded to preserve the institution of slavery, but instead was defending the rights of their states from federal overreach. Southern soldiers were no longer malnourished hicks but honorable men led by the kindly and brilliant General Robert E. Lee. Northern and Southern veterans met at battle reunions and took pictures and spoke as comrades. They conceded that while they had once fought against each other, they were now part of the same national idea. The Lost Cause took the nation by storm, infiltrating books, magazines, newspapers, and later movies. The first movie shown at the White House was Birth of a Nation in 1915, a movie about the founding of the KKK. Ever heard of Gone With the Wind? Adjusted for inflation it’s still the highest grossing film of all time and is deeply steeped in that ideology. Idolizing the confederacy was a national problem, not regional. However, it was done to pacify the South and allow them to rejoin the union. But at what cost?

This is where the racial perspective comes in. So the North was now acknowledging that Confederates were honorable adversaries and technically Americans all along, so Southerners should be happy right? Wrong. Remember the whole African Americans getting civil rights thing from paragraph two? Yeah, the South wasn’t crazy about that. So, the North basically let Southerners do what they wanted after Reconstruction ended in 1877. Across the South blacks lost rights as whites reclaimed political, economic, and social power. In the North, accepting that the Confederacy was about states rights meant forgetting the impact of slavery in starting the war and ignoring the injustices that occurred in the 100 years following the war’s conclusion. African American’s contributions to the war effort (like the US Colored Troops) were forgotten about or minimized. By 1900, African Americans were historically sidelined in a war that everyone in 1865 thought was about slavery. Blight has a whole section of his book dedicated to the efforts of some to keep the African American experience in the war alive, but they were largely drowned out by the white perspectives. So, white America reconciled by eliminating the importance of black America. Americans brainwashed themselves into misremembering the true causes and impacts of the war, but that was probably acceptable to them because the country was reunited and the only people that suffered from it were African Americans.

So, to come back to your original question, Americans even today are swayed by the confederacy because of the narratives Americans told themselves in the decades following the war. It’s a question about memory more than history. It’s why there are monuments to confederates that are outside the South (and more than you think). For a long time, they were understood to be the good guys, just like the Union. Parts of the nation woke up when they began to see the injustices that African Americans faced during the civil rights movements of the 1960s. Unfortunately the South still struggles with it today. And a lot of it has to do with how pervasive the narrative that was crafted still is. Many people still argue the Civil War was not about slavery, and even if it was, the confederate dead aren’t traitors. It’s difficult for many Southerners to admit that their ancestors are somehow tainted by a legacy that is deemed evil by today’s standards. Instead it’s easier to understand their ancestors as honorable underdogs reluctantly fighting for their farms. It’s a mischaracterization, but in a lot of places that’s still what is taught. The Lost Cause is alive and well today, simply look at the justifications against removing Confederate statues. In a lot of places it’s framed as “attacking my heritage.” Well, it’s only attacking heritage if you understand your ancestors to be the heroes that they framed themselves to be after the fact. How many people would want to idealize their ancestors if they understood them to be bad people?

As I said there are a lot of other books on this subject, but Blight’s was one of the first to tackle the history of Civil War memory, which is how people remember and interpret the war, not necessarily what actually happened.

Honestly u/Madmax2356 covered a significant portion of the issue. I just want to add one other aspect that I find fascinating.

Tony Horwitz released a book, “Confederates in the Attic,” in the early 1990s. In it, he talks about the modern living experience in the South that demonstrates a continuation of the Confederate lifestyle in modern history. (Definitely recommend this book).

A significant aspect of his work that stuck out to me was how he approached the familial pride. From the time of the colonists, the south built strong familial communities, with ‘blue blood’ and a legacy passed down through the family units. A name had a significant amount of weight. Even after the Civil War, the south still maintained a loyalty to their family history, which wasn’t replicated in the North, as many immigrants and freed slaves flooded to the North. This meant that the south generally remained directly connected to the Confederacy, whether as veterans and their families or descendants of.

This rather homogenous environment meant that the feelings fostered and were never quite resolved. To some who can trace their lineage back to Confederate soldiers, these last 150 years have not been a period of moving forward and shaping a new, modern society. These last 150 years have rather been a ceasefire - to some, the war is not yet over.

In your question, you say the Confederacy only lasted 5 years. And from the point of the war, you’re right. But from the beginning, many in the south saw all the events as a direct attack on their way of life. These feelings of unresolved justice have still been perpetuated today. From this perspective, it’s not something definite in the last 150 years. It’s rather the family loyalty and belief that has been passed down for generations that the south should not have lost, that the war is not over, that their basic rights and lifestyle was under attack, and that maybe, one day, the Confederacy will again be seen as a source of pride. Many see it acceptable to remain loyal, because that is their family and their history. The book talks about people who follow Civil War events more closely than a religion, where children are taught of the Civil War history and lineage from a very young age. To them, it is acceptable because it’s their history and their identity.

Again, I highly recommend Horwitz’s book - it highlights a interesting interpersonal viewpoint of the Civil War and the resulting emotions.