Today, the city of Jerusalem is seen as so important that people are willing to kill and die to control it. And that struggle goes back centuries. Nearly a thousand years ago, European Christians embarked on what became known as the First Crusade: an unprecedented, massive military campaign to take Jerusalem from Muslims and claim the holy city for themselves. They won a shocking victory – but it didn’t last. A Muslim leader named Saladin raised an army to take the city back. What happened next was one of the most consequential battles of the Middle Ages: A battle that would forever change …