I like the T-shirt with Geronimo and his friends on it that says  "Fighting Terrorism Since 1492".

Of course, a little history of the "French and Indian Wars" and the atrocities on both sides of that one is instructive.   

The movie "The Patriot" hints at some history on both sides of that one!

"Atrocities breed atrocities" is a fact for several thousand years of human history up to and including our own times today. 

 Show me a 'war' involving deaths and I will show you an atrocity on both or even multiple sides of that very same 'war'.