The Great Big Book Of Horrible Things: The Definitive Chronicle of History's Worst Atrocities by Matthew White. My brother has this book in his bathroom. I got it from the library. I suggest that you buy it.
White walks through, in chronological order, the recorded kilodeaths and megadeaths that humanity has inflicted upon itself. It would be very easy to be cynical about this, and the antidote for cynicism is a morbid sense of humor. White possesses this. Not quite as developed a sense of humor as James Mahaffey, but it will suffice.
I could sample and excerpt some of the more awful things (like, for example, the peculiar Chinese execution practice of death by slicing), but instead let us look at his criteria (explained at the end of the book), and then also some of his general observations.
Upon finishing this book, I observed to my brother "We're just ants aren't we?"
Fire ants or crazy ants, it really doesn't matter, but from the historical perspective of 10,000 feet up, yup, we're just ants. Bugs. Ape-shaped bugs. You would think, with big primate brains acting in the aggregate, that we'd be smarter, but nope. There seems to be a limit to, or a cyclical referent to, the sophistication collective behaviors, and as such it makes me hold no great hopes for the coming hyper-neural network collective of hyperintelligent computers and the great Global Hive Mind. Megadeaths? Gigadeaths, or given a colonizing push out into space, teradeaths.
But you have to have a sense of humor about it. Couple of things. Anyone who ends up with the title "the Great" murdered a lot of people to earn that title. Oh, wait sorry, criteria.
In order to make it into the book:
1) there has to be an immediate or closely followed death toll above 300K
2) a result of a specific outbreak of coordinated human violence and coercion
3) deaths can be direct (war, murder, execution) and indirect (aggravated disease, famine, accidental or incidental killings of civilians).
That's it. Quibble if you want, or write your own book.
Worse guy in history? Hitler*, of course. Or sure, Stalin was a monster, Mao, Pol Pot, etc. Alexander the Great was an asshole, along with Napoleon, Timur, Qin Shi Huang Di, etc. But Hitler deliberately and calculatedly did what he did in a way no one else has come close to doing... yet.
Badasses of history? Hardly killed anyone. Vikings, Huns, Samurai, Sikhs, Spartans, all light weights. You know who tops the list in multicides? The French. Yes, those cheese-eating surrender monkeys. Followed by the Chinese, the British, Russians, Germans, Americans. America better get cracking.
Terrorism. A problem? Small potatoes. To really kill a lot of people apparently requires the appartus of the state. Want to see a lot of deaths? Declare war on terrorism.
Justice? Most asshole dictators die comfortably in bed.
Sieges kill more people than battles do.
In war, civilians die more often than military. Want to be safe in war? Surround yourself with an army.
Chaos kills more often than tyranny. Failed states and the breakdown of authority account for more mulitcides than abuse of authority.
Religion kills? I got news for you, people were being nasty to each other long before religion came along. Percent of total human suffering caused by religious wars and persecutions? 10%. Or about the same as atheists have done. Take that, Richard Dawkins.
Hereditary monarchs are usually too inbred stupid to cause much trouble. If you want to get truly talented murderers to do a proper job, set up a meritocracy.
Guerrilla war. No state has ever managed to come up with a solution of organized versus irregular militia. It seems the only solution to insurgents is to set up a competing guerrilla band and let them hunt each other. (Lesson that municipalities learned in dealing with gang violence, perhaps???)
Finally, if you want to look at the illusion of progress (*cough* Pinker! *cough*), keep in mind that the 20th century was the bloodiest ever. White goes so far as to come up with a neologism to describe it: The Hemoclysm, the blood flood. 150 million dead. Well, fear not, this century is early. Maybe we'll have a new term by the end: The Coproclysm.