Not really. The American Civil War ended chattel slavery. World War II ended German Nazism and stopped the Holocaust.
Neither is a good example:
-- The United States was not the aggressor in the American Civil War, the Confederacy was. If it hadn't been for the determination of the "slaveocracy" to start a counterrevolution, posing as a revolution, for the sake of protecting chattel slavery, and propagating slavery into the new territories as well as, they hoped, the free states (Fugitive Slave Act, Dred Scott decision), there would have been no secession, no firing on Fort Sumter, no war. Therefore, that war was pointless, because chattel slavery was not a just cause. The Johnny Rebs were on the wrong side of history.
-- The Nazis were clearly the aggressor in World War II. Though they did have one or two legitimate gripes-- the excesses of the Versailles treaty, chiefly-- those could have and should have been addressed by peaceful means. Again, a hideously pointless aggression.
And there have been many wars of rebellion that have overthrown either particular governments or entire social systems so as to improve the conditions of the people for the better...
You're on much more solid ground here. I certainly wouldn't want to take back the American Revolution, even if our Founding Fathers didn't have nearly as solid a case against George III as, say, the slaves in Haiti did. It's difficult to imagine how the Haitian revolution could have been accomplished without any violence, but as you know the rest of the world has been punishing the Haitians ever since, 'cause, like, they're the wrong color and all, know what I mean? (Please excuse my cynicism.)
however, point to the establishment of modern India as an example of a revolution that was accomplished almost entirely by means of nonviolent resistance. At least in some times and places, it can
be done. The fall of the Soviet Union was also done with very little violence. As for secessions, which are arguably sometimes necessary and just, the splitting of Czechoslovakia was conducted by referendum. By comparison, a violent secession by either Czechs or Slovaks would then be viewable by us as pointless, because it obviously could have been done without bloodshed.
...Which brings us back to World War I, the subject of the present film. Franz Joseph and the Austro-Hungarian military wanted to add Serbia to their collection. So they issued an ultimatum that they knew the Serbians would have to be crazy to agree with. Look what happened. Pointless, pointless, pointless.
"I don't deduce, I observe."