Every big country I can name that has existed for more than 150 years or so has had a civil war. The effects of which often spill out onto other countries. I'm thinking about the American Civil War, which raged from 1860 - 1865, primarily over the rights of the states that compose the country, tariffs, and as pulp history likes to over-simplify it, the legitimacy of slavery as an institution. The war ended with the complete defeat of the southern rebels, "Dixie," and a rough period in which they were reintegrated into the country. Historians like to point out the weird parallels with America's war of independence in the first place, with the northern faction more in the position of the UK and the southern faction more in the position that the colonies had at the time.
"Dixie," or as it officially named itself The Confederate States of America, had pinned its hopes of survival on the UK and France intervening in the war. Such a foreign intervention is a major risk for the intervening power, as a successful intervention leaves the surviving power in their debt, but a failed one leads to understandable anger from the faction you opposed. The Confederacy ultimately sucked at diplomacy, and their "You need us as we're your biggest source of cotton" position alienated the countries they wished to court, who promptly found other sources of cotton to feed their mills.
I'm aware of the take of the UK, France, and Mexico on the affair. The UK and France were horrified by the Confederacy's enthusiastic endorsement of slavery, an institution that they had both recently banned as grossly immoral. They were also aware that friendly actions towards the Confederacy understandably cheesed off the American government, which was a major trading partner of theirs. Mexico, meanwhile, had lost half of its territory to the Mexican-American war twenty years before, and was aware that the Union government had no further claims, while the Confederacy desired the remainder of their lands. They were grateful to Abraham Lincoln (the Union president)'s denouncement of the Mexican-American war as a cynical land-grab, and was thus enthusiastically pro-Union.
I'm curious as to how the rest of the world felt about the Confederacy, then and now, especially as a lot of conservative southern Americans look back to the Confederacy with nostalgia, and even vigorously wave Confederate flags and dream of a repeat. A behavior that northerners and westerners find treasonous. As late as World War 2, southern battalions often incorporated Confederate symbols where possible, and the American visit to Mao was called the "Dixie mission," comparing his rebellion against the Republic of China to the Confederate rebellion against America. Except that Mao was a left-wing communist and the Confederacy right wing extremist, and Mao actually succeeded, an interesting comparison.