Question: How do we know Hitler is not the Antichrist?

Answer: Hitler was not the Antichrist.  This is clear because the prophecies concerning the Antichrist remain unfulfilled.  For example, look at 2 Thessalonians 2:3-10 and Revelation 13:2-8.  We see that the coming Antichrist will seat himself in the temple and declare himself to be God.  He will perform signs and false miracles to convince people of his claims.  He will even appear to have come back to life from the dead.  He will be killed by the Lord, without human agency, when Christ returns.   None of these things found fulfillment in Hitler, so he cannot have been the Antichrist.  But, as Paul says, “the mystery of lawlessness is already at work” (2 Thess 2:7).  Evil men will come, “even now many antichrists have arisen” (1 Jn 2:18), but they will all be eclipsed by the man of lawlessness (the Antichrist) described in Scripture.