there is a very good documentary on Neflix called "The Civil War" by Ken Burns, and it is an 8 part documentary and it talks all about the Civil War.
It would take too long for me to explain everything about the entire Civil War, but to summarize it, when the North and South were divided back in the mid 1800's, they had the Union in the North and the Confederacy in the South. The North was free, and the South had slavery. Then the 13th amendment was added to the Constitution which officially abolished slavery, but the southern states did not want it, so they exercised their right to secede, which means they broke away from the Union. Even today any state in the country could do it if they wanted to, according to the Constitution.
But anyway, when General Lee surrendered to the North, the country was unified. But let's get a few things straight. First, it is not called the 'hate flag', it's not called the 'racist flag', or anything like that. In fact, it is actually not even called the Confederate Flag, it's called the Battle Flag (or sometimes called the Rebel Flag). The 13 stars on the flag represent the 13 states that exercised their right to secession (or to put it another way, state's rights). And the flag has the same colors as the current American flag. But it is a symbol of our history and our heritage.
the reason that there is controversy over the flag in modern day society, is because unfortunately a lot of people who fly the flag don't do it to show their freedom, they do it because they are racist. Now, in my opinion, I think that is totally wrong, but it is also their right. Racism is wrong in my opinion, but it is not against the law. But also when that pastor was shot by someone who was flying that flag, it added to the concern that people had. And then of course there have been a lot of movies where it was used as well (for example "A Time To Kill" had those 2 white rednecks who had it in back window of their truck).
But you can't blame it on a flag. If you want to blame someone, blame the people who fly it out of hatred, and also suggest to them that they take a history class and learn about what the flag is really about. I think that people who fly the flag should make sure that they are doing it for the right reasons.
I also feel that taking it down at Fort Sumter, where the first shots were fired during the Civil War, is disrespectful to our country, because that is a historical monument and you don't interfere with history. As tragic as it may have been, we need to have ways to understand what happened, and we can't just pretend like it didn't happen.
I hope this helps...