Who caused more death/destruction in human history? A. People acting in the name of Christianity or B. people acting in the name of atheism?

Wrong question. The correct question is who caused more death/destruction in human history? A. Actual Christians or B. Actual atheists.

Anybody can claim a title, but it is meaningless if it isn't in truth. That would be deceptive.

No one has ever caused any death/destruction 'in the name of atheism', so that should answer your question for those who don't already know.

The only person in history who had the authority to answer such a question told religious zealots:

"You are from your father the devil and you do the lusts of your father. He was a murderer from the beginning and abode not in the truth because there is no truth in him. When he speaks a lie, he speaks of his own: for he is a liar and the father of lies." (John 8:44)

Weigh up how much murder has been committed since the start of human history, and you have the measure of satan the devil. He has caused more death and destruction in human history than any human group. The question is, which human group has satan the devil as their 'father'?

No one "acts" in the name of atheism.

Christianity is just one religion of many religions and deities that the theist had made... It is quite understandable why primitive people, who were so much more exposed to the overpowering forces of nature than we are today, should have personified these forces in fear and trembling, and for millions of years they do a lot of death of destruction in human history all of them including Christianity, got a few genocides made in the name of their gods...

Nobody does things in the name of atheism, that isn't a motivating factor in someones actions.

Almost certainly Christianity.

But even if it was atheism, there would still be no compelling evidence of any gods.

If something is done in the name of communism, or Stalinism, or Maoism - is that then in the "name of atheism"? Sure these guys persecuted people because of their religion - but they also persecuted atheists who thought or acted the "wrong" way.

When the Christian Catholics wiped out the Christian Gnostics - was that in the name of Christianity? What about when the Protestants and Catholics were killing each other for the last 400 years? was that for Christianity? Or for political power?

The answer is that the most destruction has been caused by people. Those people use whatever easy excuse they can lay their hands on o separate US from THEM, so that we can feel justified for killing them so that some leader can gain power and influence.

I would say neither. The most destruction was caused by people acting in the name of racism, their king, Caesar, country, emperor, fuhrer, or socioeconomic/political system.

People who chose to do their own will instead of doing the will of the Father.