Secession set up the Civil War, but it was cannon fire that started it. The colonies didn't like Great Britain much (or at least some of the things GB was doing), but it wasn't until Lexington and Concord that it was a Revolution. It was an armada of Japanese bombers that brought the United States into the second World War, and it was two very big bombs that ended that war. Guns may or may not kill people (we'll leave that to the bumper sticker writers to decide), but the bullets sure do.
The American Civil War, by comparison with other civil wars in world history, was a relatively small affair. China's myriad rebellions in the same century took millions of lives, but our Civil War killed less than 700,000 (or slightly more depending on the source). Civilian casualties during the Russian Civil War exceeded 13 million, and that's before we start counting soldiers. And yet, in many ways, the American Civil War was more brutal than anything that had come before it.
Using battlefield tactics dating from the Napoleonic Wars, line after line of soldiers marched at line after line of other soldiers. When muskets were in use, this was an effective strategy because the weapons were horribly inaccurate unless at very close range. But then we found rifles.
The rifled musket added two things to the musket -- range and accuracy. Now, our line after line is getting picked apart from hundreds of yards away, but they continue to march forward into the leaden hail. Thus the casualties from the American Civil War exponentially grew as rifles replaced muskets. (Despite the new technology, disease remained the biggest killer in the war, but that's the subject of another post.)
In September, Riddick's Folly will install a new, permanent exhibit displaying more than a hundred weapons used in the Civil War. These pieces -- rifles, pistols, and swords -- trace the evolution of weapons engineering from the antebellum to Antietam to Appomatox. Come and check it out. It will be worth the trip.