The actual body count of Stalin's victims is almost equal to the total amount of people dying in World War II

The body count of Stalin’s victims before and after World War II is estimated by scholars to be anywhere between 20 million to 60 million people, but roughly 33 percent of young Americans still seem to think Mr. Bush’s time in the White House was deadlier.

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George W. Bush viewed by one-third of millennial as bigger killer than Stalin: Poll

If you think clearly about the number of people who died because of the Iraq War starting around 2003 I believe it would be presently around 100,000 to 500,000 people I presently believe. However, so many many people were killed in secret and buried in people's back yards in the sand or left in the desert to rot it is really hard to say. It was never safe enough for anyone to run around and actually check how many people actually died in Iraq from 2003 until the Americans left pretty much around 2011.

Whereas it is easy to say that Stalin killed 20 million to 60 million people because there were witnesses to most of these deaths. However, now, most of those have already died of old age or war as well so this is one reason why millennials don't know as much about all this.