It was not "the thinking of the time." It was the thinking of a small group in a minority of the states of one country, a country that looked to Europe for its standards. What would befall a British, or Prussian, or Austrian, or French general who made war against his own king and lost?
Wouldn't be no statues, that's for damn sure.
Like Napoleon?
The whole of the southern states seceded in the US Civil War. There were enough to wage a long protracted war and England (although neutral) leaned towards the Confederacy regardless of their views on slavery.