Michael
2,000 Years of Chinese History! The Mandate of Heaven and Confucius: World History #7. Buddha and Ashoka: Crash Course World History #6. The Persians & Greeks: Crash Course World History #5. Mesopotamia: Crash Course World History #3. Indus Valley Civilization: Crash Course World History #2. The 5 Most Terrifying Civilizations In The History of the World. They say that those who ignore history are doomed to repeat it, so pay attention for Christ's sake.
It turns out that many of our ancestors achieved levels of violence that take them right out of the realm of "badass" and into the less cool area of ball-shriveling atrocity. These are the civilizations you don't want to face during, say, your next time travel adventure. And yes, the Spartans are down there. History is kind of spotty on the Celts (they never wrote anything down, and many of the witnesses died brutally) but what facts survived confirm one thing: They had gigantic Celtic balls.