Comment by kjellsbells

The fourth crusade was wild.

- let's go and reclaim Jerusalem from those non-Christian infidels!

- Sure. We're gonna need a bigger boat. Let's ask the Venetians.

- Here are your ships, guys.

- Err, we have no money.

- Sigh. ok. Go and attack our rivals over there.

- The byzantines in Constantinople? They're Christian.

- You want something to do, or not?

- Fine. let's kill them all, boys.

Result: Constantinople is ravaged. Byzantine Empire fatally weakened. Ottomans take the city 200 years later.