What justifies the Crusades, and do they contradict Christ's teaching?

The Crusades had their good points and bad points. Anytime you raise swords in the name of the Church there is a question about the motives and justification; in self-defense it is justified, but even then with limits. The main purpose was to free Jerusalem from the foreign hordes that had overrun it, because Jerusalem has a built-in Christian heritage; it is where the Church began at Pentecost and where our Lord was crucified. But I am leery of defending the Crusades, because when you end up with dead bodies all along the road and in Jerusalem, you have to sit back and ask whether that is really what God wanted, rather than wielding the Bible. It is too easy for the Church to get caught up in physical things and forget why we are really here.