I'm not whitewashing anything. The world is better off because of us. Not every single individual in that world. True.
You take the good with the bad. I absolutely want the US to engage in much less use of force worldwide, but those situations and areas were shitty before we got involved, and that despite our best efforts they are still shitty isn't entirely our fault. Should we have stayed out? Yes.
If you see someone brutally beating their child in a restaurant, would you intercede? Don't you have to? I think the US is much better off because the rest of the world stood by and let us work it out ourselves. The mistake we're making globally is not letting that happen elsewhere. Pretty glad the French gave us all that gunpowder though.
Are our motives always that pure? For many of the people involved, yes. Are there always folks there with ulterior motives? Yes.
Slavery in the South is indefensible. Comparing it to slavery elsewhere in the world is a false choice. Slavery was way worse in the South. In most of the world, slavery is alot closer to indentured servitude, which is how it got started in the American colonies. It evolved in southern plantations into something that boggles the mind with its abject and brutal subjugation. That's why I say it is possibly the most horrible thing that has ever happened. And it got worse and worse every year. So ending it was as much about stopping the escalation of the awfulness as anything else. Southern slavery was not just entrenched and awful, it was getting worse.
And there is no way that the majority of soldiers fighting for either side really knew what it was like. Abolitionists were so vocal in their advocation of an end to it because it was so bad, but very few people spent that much time at a plantation. And there was no wikipedia, not many books with photographs.
There is literally no other group of people in the history of the world that were treated as badly as the plantation slave in the South. None. It is a testament to the strength of the human spirit that slavery didn't end with massive and widespread suicide.
The lasting legacy of southern slavery is that it set a new low for what the human race would do to itself. From wikipedia:
"Even though slavery is now outlawed in every country, the number of slaves today is estimated as between 12 million and 29.8 million."
Rest assured that every one of those 29.8 million current slaves is better off than a slave in the American South.
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As to the start of the war, the confederate states seceded, which they believed was their legal right. The north disagreed, including several states that would later join the confederacy. Federal troops stationed in South Carolina were asked to leave. They declined, and were fired upon. None were killed though (granted this is a stupid point to make, as firing artillery like that is clear intent to kill). Lincoln called for every state to provide troops to retake the fort. So the official declaration of war was both sides cracking under the stress. In retrospect, federal troops and assets should have withdrawn from the South, or at least made it look like they were planning to withdraw. And the South should have given them a little bit more time to come to that conclusion. Who declared war? Foreign troops on your sovereign soil is an act of war, period. Insofar as there are laws governing that, this is a universally understood fact. Lincoln calling for troops to retake the fort caused more states to secede, and precipitated Lincoln doing something abysmally awful in Maryland. Lincolns refusal to acknowledge the reality that the South had left the union is as much to blame as the South actually leaving. If the South had seceded over the right to have peanut butter, Lincoln would have reacted the same. To argue that it wasn't about the North's view that leaving the union is prohibited, a concept that existed in no law or custom, is to misrepresent the historical reality. The epithet hurled at southerners during the war was not slaver. It was secessionist.
The "invasion" of confederate troops into Maryland: then a slave state (in which slavery was legal and ongoing even after the emancipation proclamation, which freed 0 actual slaves as it applied only where the U.S. was not in control), was kept from officially seceding because Lincoln suspended the rule of law, and abused his authority to incarcerate law-abiding american citizens. He did this for strategic reasons, D.C. would have been totally surrounded. Maryland was at most a literal battleground state, occupied by union forces, but loyal to the confederate cause (had Lincoln allowed it to self-determine, it would have gone confederate).
Given that slavery was on its way out economically, as slave labor can't compete with industrial advancements, there probably was a peaceful path. Slavery in the south was so bad though, if anything even close to it existed today, I'd be pushing for the U.S. to invade and end it. I think the South was right in their interpretation of states rights, and Lincoln marks the last president of the original American experiment, and the beginning of the Federally Incorporated States of America. I also think the South picked the absolute worst issue to try and stand up for.
To say that the flag represents slavery though, is wrong. It's not the flag of slavery. If you choose to have it represent that, then fine. That's your choice. It represents alot of other things. If you think it is borne with absolutely no shame, you are wrong.
I have the right to go to any public building I want and raise whatever flag I want. Nobody has to leave it there and nobody has to like it. Aside from a few people like Lincoln, who didn't respect the rule of law, most agree the constitution affords me the freedom of speech, of expression.
The American Civil War was awful. Neither side was right. The Northern histories like to tell a story where they were anti-slavery, but the true history is that slavery is an American moral stain. The reason it's called the last battle of the american revolution is that 80 years before the civil war they knew slavery was a problem. I don't agree that the South should have been allowed to work it out on their own, but I like to think there was a better option than 600,000 american soldiers dead. Slavery was so terrible, ending the practice would have absolutely been worth any multiple of that number. No man knows freedom if any man doesn't.
We can wish those who came before us never made mistakes, and we can try and learn as much as possible from those mistakes.
Burying the history is counterproductive though, it's book burning and knowledge destroying. There is a consequence in enforcing your will on others. Persuasion is always, always the better option. Agree to disagree is not always going to be acceptable, and so you get human rights wars. It is a bizarre and horrifying reality that war can be used to advance humanitarian ends. Considering that war represents the breakdown of any humanitarian considerations.