That's some serious squinting you are doing there. Square peg into a round hole. Although neither side necessarily sold the war on these terms, the American Civil War was fought over slavery. And by "fought over slavery" I mean specifically that it was fought over the ethical and normative value of slavery, which happened precisely because the national cultural value was supposed to be "all men are created equal...". The north would have had no problem with slavery as an economic institution if it did not have a significant population that opposed it for moral and religious grounds.
You can't put two different cultures into the same nation, so by 1860 you had a situation where you had two nations trying to live under the same political umbrella and the South's move to secede only was a final acknowledgement of that reality. It wasn't fought over population pressure, and none of your evidence actually links up. You gave a series of stand alone sentences that neither support each other or your thesis. The South wanted to expand into the Western territories, not because it was feeling crowded, but because it needed additional leverage in the democracy. The South was perfectly willing to forgo all Western territories if by doing so it could secure it's culture from political intrusion. The burgeoning population of the North wasn't an economic crisis for the South, but a political crisis because it gave the North more votes and it knew that eventually those votes would be used to try to forcefully dissolve the South's economic institutions. But it wasn't like the South feared the North wanted it's land or the South thought that more Northerners was a bad thing in and of itself, because the North was among other things a market for its goods.
It's absolutely ridiculous to assert the North would have been destitute without the South. The Civil War itself proved that. The North could have afforded to let the South go from an economic perspective. The North's economy was massive compared to the South, because the South for a variety of reasons from slavery itself to climate had not industrialized (the South didn't actually explode in prosperity until air conditioning came along). New York alone had a larger economy than all the states of the Confederacy. Nothing the South provided was irreplaceable, because the economy was global. The North could have and did import cotton and beef and so forth from other suppliers without so much as blinking. Your assessment of the war seems grounded in the Southern leaders pre-war assessment of the war, and not the war as it actually was. I think it is very valuable to teach the American Civil War from a Southern perspective, but you seem to take that a bit too far.
We're going to have to agree to disagree. The moral nature of slavery was, at best, a bottom tier reason for the war. You touched on the one of the primary reasons, but didn't fully explore it -- the political power of the slave states due to the 3/5th compromise. The North wanted to prevent more slave states because the slave states wielded undue political power because of how the 3/5th rule worked to allow the South control of the House. More slave states would continue this trend, and the North desperately wanted to pass legislation that aided the non-slave states economically and politically but were halted by the slave states.
Economically, the South still brought in the lion's share of the money through trade. As I noted, a decade or so would have inverted this, but, at the time of the war, the South was a prize economically. The value of the slave economy was greater than the entire industrialized footprint of the whole Union at the time of the civil war and cotton prices were soaring. The South was an economic powerhouse that was larger than the North. However, the basis of that wealth was very different, and, as you note, the result of the war was largely due to the basis of the economy. The slave-agrarian economy of the South was ill-suited to support a war and continue to make money, while the industrializing economy of the North could. But, no, sorry, the South was a huge economy and the split incurred huge losses in income for the government due to the loss of the cotton trade. It was imperative that the value be retained AND that a strong competitor for westward expansion be curtailed. The preservation of the Union, while high on Lincoln's personal values, wasn't a strong reason for the rest of the Union to engage in a shooting war with the South.
And, to go back to the moral issue of slavery, abolitionists were a small fraction of the political movement in the North. Lincoln himself held rather, um, distasteful views on the issue of slavery and was against abolition. Over the course of the war, he moved greatly, but when he started the war the ending of slavery was not one of his objectives. The Proclamation, as a matter of fact, was a PR and psy-ops effort rather than a statement of moral clarity.
So, population pressure -- the core crux of the political argument over slavery was westward expansion, something that the US was very keen on to move more population into more gainful use. The conflict was how that was to be used, but more free men (and therefore more individual use) or by the continuing of the African slave trade and the slave-economy, which limited the gainful use of free men by it's nature. This was the crux of the war -- how the country would expand westward, and population pressure is central to that crux.
Again, slavery is bad, the South needed to lose the war, and whatever other caveats are needed to excuse a dry and distasteful examination of the Civil War and it's complex causes.
You are speaking too soon. China is well on its way to picking a fight. It's just looking around for a good excuse and a likely target. It's pretty much acting just like I'd expect a newly prosperous nation to act. It's trying to acquire assets in Africa, trying to gain overseas territory for naval purposes, and expanding its hitherto primarily defensive military assets into more and more aggressive assets that you need to assert military supremacy far from your homeland. The only reason it hasn't tried to take Taiwan already is its concerned the USA would intervene, but it's trying to box the US Navy out of the area in an attempt to gain enough 'breathing room' to do an invasion quickly and force the USA to accept it as a fait accompli.
But let's try to stay away from modern examples, and stick to history. Some of the most aggressively expansionistic nations in history were the Athenian Republic, the Roman Republic, the British, and the USA. Athens was the aggressor nation in the Peloponnesian War. Rome was the aggressor nation in the Punic Wars, and let's not forget that Carthage was itself a product of a highly expansionistic and aggressive Phoenician Empire. Most people, including most Americans, looking at American military history get things exactly backwards. Pretty much every war the USA was involved in during the first 100 years, the USA was the aggressor in. We started pretty much all of them. After the US Civil War, the explosion of prosperity directly led to America's most blatantly imperialistic behavior in the Spanish-American war. The USA certainly wasn't short of land to exploit at the time. However, almost every war that the USA has fought since the beginning of the 20th century has been defensive in nature. Most people get this backwards, treating the young nation as simply defending its interest, and the more developed nation as being aggressively imperial. The facts go exactly the other direction. In point of fact, newly wealthy nations try to dominate less wealthy nations simply because they can, and newly wealthy Republics tend to look for excuses to go to war. France became much more aggressive as a Republic than it had been as a Monarchy, leading "World War 4" (if you count actual global wars) and between 4.5 and 7.5 million deaths (depending on your sources).
Bad pool to dismiss examples against your thesis so cavalierly.
But, sure, let's look at history. You've picked four great examples. Was Rome wealthy before it began it's conquests, or was it made wealthy by it's conquests? Same with Athens, same with the US, same with Britain (although Britain is a lousy example of a newly wealthy Republic). Athens started the Peloponnesian War, sure, but it was going to happen anyway. The US was expansive, but didn't eat any smaller countries except the Native American nations, who were, bluntly, not capable of competing due to the difference between a Stone Age culture and an industrialized culture. Not excusing the abuses, but there's limited use in describing US Westward expansion as going to war with other countries. Yes, we fought the Spanish, but, at the time, both countries were engaged in rapid expansion into the same territory -- ie competing militarily for the same new resources. Hard to describe that as a war of aggression on an established other country when the difference in arrival was measured in years and both were killing natives to grab the land, yeah?
Britain, on the other hand, well, not sure how you call a country with that much history new. Did their massive colonization efforts reap huge rewards? Sure, but Britain didn't do that in a vacuum -- the rest of Europe was involved in a massive worldwide land grab at the same time. Britain came out on top, but, then, someone had to. This kinda goes back to the US early year wars -- they were all with other colonial powers all engaged in wars of acquisition against native cultures. You're picking on the winners and holding them up as if they're special examples of how some new countries that are rich start wars, but, really, they were in wars with other countries and just happened to be the winners and thereby got rich.
So, sure, I'll squint and give you Rome and Athens, go halves on the US (it was at least new), and say nope on Britain. China's (and the rest of SE Asia, recall) are still on my example list unless you have a breaking news story to share?
