It's important to keep in mind that the Nazis were able to kill 6,000,000 Jews because those Nazis were very efficient. The basis for the killing was hatred and ideology.
Hatred and ideology are both around today as a basis for killing religious and ethnic minorities, such as dissident Syrians, Shiite Muslims, Sunni Muslims, Christians and of course Jews.
Even Buddhists get into the act, killing Muslims in Myanmar.
Other holocaust targets include immigrants of any kind, poor people, homosexuals and even simple political liberals.
A little more Nazi-style efficency would get those numbers into the millions too.