The Crusades were initiated to defend Christian lands against the invading Muslim armies. Today's Muslim terrorists have the same motives and goals as the Muslims who fought the Crusaders. Nothing has changed over the last 1300 years.
Our president invokes revisionist history to defend what the Muslim terrorists are doing in light of what some Crusaders did to the Muslims 1000 years ago.
Here are three articles on what the Crusades were
Yes, some Crusaders were wrong and did not follow the teachings of Christ (love your enemies). Mohammad's followers were doing what Mohammad taught them to do in practice and according to the Koran (kill the infidels). Still happening today.