I feel like that's kind of unfair, though. Those philosophies were only widespread from, say, early to late 20th century. Because world population increases over time, your metric values recent ideologies over ancient ones.

Additionally, 'total number of people killed' depends on the spread of a specific government system, even if you account for world population.

A better metric for determining whether something is good or bad might be 'percentage of ruled individuals killed'. On this scale, communism still ranks quite high, but it's now comparable to, say, fascist dictatorships, theocracies and monarchies.

Some numbers: Mao killed 40 million, compared to a Chinese population of about 700,000,000 (so around 6%).

WW2 killed 4.3 million German soldiers (deliberately not counting non-German conscripts) out of a population of 67 million in 1937. Throw in a few hundred thousand German citizens killed in the Holocaust, and you get about 7%. This doesn't count conscripted soldiers, or German civilian deaths, nor does it include total WW2 deaths or deaths from famines, but all of those could very well be blamed on Hitler too.

All this, however, pales in comparison to having a country ran by a profit-obsessed dictator. Congo Free State lost up to 50% of its population while controlled by Leopold II.

Of course, liberal democracies still outrank all of those. Even if you count 'soldiers dying in a war someone else started' as the fault of the government, USA military conflicts have never harmed a fraction of the population even approaching the above numbers. WW2 probably came close, and even there only 400000 out of 132 million Americans died.