- 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.