Counter-factuals
I've been reading a lot about antebellum American slavery and particularly Harriet Beecher Stowe's novel Uncle Tom's Cabin, as part of the research on BDSM history.

Looking backwards from 2008, it's easy to see American slavery as something that had to be stopped, and assume a manifest destiny assumption that it would be stopped. But I'm not a determinist, and I believe history could have unfolded some other way.

What I'm wondering is, would American slavery have ended without the violence of the Civil War? (According to Wikipedia, 620,000 casualties in total.) There's the related question of, was it morally right to go to war to end slavery, among other reasons? (How much of the Civil War was really about slavery is a debated point, but it was certainly a strong issue.) And were there preferable alternatives?

People who grappled with the question of slavery in Amerca had several potential futures in mind. Many of them did not involve assimilation of blacks into white society. Stowe, at least in her books, seemed to be in favor of recolonization. Blacks in America would return to Africa, bringing Christianity and presumably other elements of modernity, and create a new nation there. Only a handful of writers saw familial and social mingling as the solution to America's racial divide instead of a taboo.

One could argue that, in the long run, slavery as an economic and social system couldn't work, and it would have eventually broken down. Perhaps peacefully, perhaps not. The agrarian/feudal Confederate states couldn't compete economically with the industrialized Union states.  But there could have any number of intermediate cases for the position of blacks in American society that would make Jim Crow look like nothing.  Would allowing that have been "better" in some larger historical sense than four years of brutal war, more than half a million dead and cities burned to the ground?

This is the kind of thing that can be debated forever. One can cite this and other examples, like the bombing of Hiroshima and Nagasaki, or America getting involved in the European theatre of WWII, in arguments that going to war is strategically and morally justified, and the rationales for the Iraq war go by just that. Invading Iraq would end a monstrous regime and stabilize the region, we were told.

The outcome, however, is somewhat different. People who practice statecraft are very much in the business of making history, of planning the fate of nations. Sometimes that has positive outcomes, and sometimes it doesn't. Even if those who decide are not compromised or corrupt, there are so many variables that there are no guarantees. We may never know what the leaders of post-Saddam Iraq decided or failed to decide.

If we can't predict the outcome of large scale actions without a reasonable degree of accuracy, how do we decide?