Facts don’t matter much in threads on this subject, but I’ll give some anyway, and I’ll remain objective rather than not reopen the argument:
As has been pointed out God knows how many times by now, what’s called “the rebel flag” in these threads was never the flag of the Confederacy. Variations on it (usually square in shape) were used as battle flags by a number of Confederate regiments. Most returning Confederate veterans generally wanted to forget the flag and forget the war, so its usage died down for a generation or two.
Now then young feller… most reb outfits back in them days deceerated their flags with the name of the unit and the names of the battles in which they’d fought, and it wasn’t at all uncommon for a company within a regiment to have its own flag. For example, the 6th Kentucky Cavalry had this flag though the brigade of which they were a part flew this one. Now, that same brigade included the 3rd Kentucky Cavalry, whose regimental flag is (like most Confederate regimental flags) no longer in existence, but looked very similar to that of the 6th (the St. Andrews cross with stars and with . At one point the 3rd Kentucky was commanded by a colonel named Jacob Wark “Roarin’ Jake” Griffith, whose brothers fought in the 6th, and the 3rd and the 6th had similar stars and bars flags.
“Roarin’ Jake” was seriously wounded in the war, but he survived, returned to his wife Mary, and had a large family. His sixth son, David Llewellyn Wark, was born in 1875. He idolized his father, all the more so after the Colonel died when David was 10, and constantly begged his uncles and other relatives for tales of his father’s bravery during the war. When he moved to NYC to seek his fortune, dropping the Llewellyn to become just plain D. W. Griffith, he used the battle flags of his father’s unit and his uncles units in his movie Birth of a Nation. (Beginning around 3:40 in this clip you’ll see three flags of the Kentucky Volunteers Brigade (nicknamed “the Kentucky Orphans”) which included the 3rd, 6th, and other regiments, and one of the flags of course is the famous “rebel flag”. It’s elsewhere in the movie as well during the battlefield scenes (considered probably the most accurate Civil War battlefield scenes ever filmed incidentally; there were actually Civil War veterans among the extras who were used as consultants).
BIRTH OF A NATION was a huge hit (not just in the south but across the nation and the world) and led to a renaissance of Confederate memorabilia, especially as most of the veterans of the war were dead or very old and the world had changed six times (telephones, cars, electricity, etc.) and this gave a nostalgia not unlike WW2 underwent at the time of SAVING PRIVATE RYAN. So, Confederate iconography became huge (not that it had ever completely gone away). Also the KKK, largely dead by this time, was pretty much reborn, and not just in the south (in fact, the Mid-west and the northeast not only got their first chapters but… well, you can look it up).
So what’s called the rebel flag became pretty big around this time, especially on college campuses. In Tuscaloosa it was for several years the unofficial symbol of the University of Alabama football team and was waved at all the games, partly because of the “Crimson Tide” nickname (which came about due to a muddy game with Auburn in 1907) and partly because of the school’s history (the U. of AL was called “The West Point of the South” and trained cadets until it was captured and burned in the last week of the Civil War) and the flag was never waved more enthusiastically of course than when UA played a northern (or at least non-southern) team. Most famous was the 1926 Rose Bowl, in which the University of Alabama defeated the University of Washington in a major upset and the next day it’s said that rebel flags were flying all over the city of Pasadena and all across the nation, hung by Bama fans and fans who were glad to see UW defeated.
So, short story, that flag was extremely popular long before the Civil Rights Era. It was featured very prominently in the movie GONE WITH THE WIND and in the promotion of GONE WITH THE WIND (it was hung from one end of Atlanta to the other in 1939) and it was probably in this time that most people began believing it was the Confederate flag, since it’s the one everyone knew. (Dixie also had a renaissance around this time- it wasn’t sung that much by the end of the 19th century, but picked up again after films started using it.)
So, in 1926 any college football fan (we’re talking millions of people) would have recognized the flag. By 1940 it was the de-facto Confederate flag. As mentioned, it was used in World War II and not just on the planes and tanks manned by southerners (in fact Air Corps General Nathan B. Forrest III famously downplayed any mention of his famous grandfather or the Confederacy [he was basically sick of hearing comments on his ancestry]). In Toccoa some units also used a version of the Rebel Yell, though it’s unknown how accurate it was ( very loud audio file of a Confederate veteran performing the yell in old age- imagine it with the energy of a young man and then multiply it by about 3,000 for full effect as to how it sounded on a battlefield).
So while there’s no question it was waved more in the 1950s, it was a southern icon LONG before then, though due more to motion pictures and football than to an unbroken line from the Civil War onward.