The Crusades were about opium.
Many medieval Europeans, especially royalty and other upper class europeans, were addicted to opium. The Crusades were actually about opium addicted europeans invading the middle east to get opium. Religion is just used to cover up this fact.
The spice trade was actually about opium as well.
Because historians lie by omission there is a good chance that the real reason why ancient romans invaded the middle east was because ancient romans were addicted to opium and wanted to get opium by invading the middle east.