2. The Crusades were a response to 500 years aggressive conquest from various Muslims. It is easy to find the march of the Caliphates from around 650-nearly 1100 when the First Crusade came about. All of North Africa, Spain, much of France, and frequent forays into eastern and western Europe.
This doesn't mean every Christian was a Saint, or that every Muslim was a horror. But the Eastern Church was crying out for aid, and eventually, some came.
You can see this playing out today. Sudan asking for help in their struggle pitting Christian and Pagans against Muslims. Nigeria's struggling against Boko Haram, al Qaeda in the Middle East, ISIS working in Iraq and Syria, Iran's sponsorship of terror in proxy wars against... nearly everyone.