There are Americans who think the Civil War was avoidable, or even imposed by the North. This new book is the latest to make the claim. I dabble as a historian when I'm not dabbling as a science writer, and I can't visualize how events could realistically have unfolded other than they did.
In 1861, the Southern states would not yield on the right to bring slaves into Federal territories, as per the Dred Scott decision, and the nation had just elected a President and a Congressional majority that, while not posed to outlaw slavery where it existed, had promised not to permit slavery in the territories. Well-meaning suggestions like the Crittenden Compromise were built on air: while issues of federalism, states' rights, etc. stoked the flames of the war, the extension of slavery was a central point on which neither side would compromise. (Don't read what Confederate leaders wrote after the war insisting slavery was a side issue: read what they said and wrote in 1861, when they were adamant it was THE issue.) Most Yankee soldiers joined the army to preserve the Union, and most Confederates to fight for for states' rights and independence, but everything except the extension of slavery could have been compromised on.) My point is that we need to be very careful in revising history: such action is sometimes justified, but not here.