Faith system in which the believer follows Christ and obeys His commandments.
Todd believes on Christ and follows Christ's example, therefore Todd is a Christian and part of Christianity
Hitler was not following Christ's example or obeying His commandments. Therefore Hitler wasn't Christian. He was a wolf in sheep's clothing and was not a true subscriber of Christianity.
Some politicians try to use Christianity to justify their actions and/or gain popularity.
Atheism is the lack of belief in God, or the belief there is no God. Depending on the atheist.
There have been subscribers of atheism that made communism did mass killings far greater than the Vatican, which isn't even Christian. Mao, Stalin, Lenin, Castro are just a few atheistic dictators who committed mass murder. Please don't say Christianity causes wars, because that's simply not true.