How is that possible if more than 99% of the more than 1.6 billion Muslims in the world aren't engaging in violent jihad? If violence is the religious duty of Muslims, then why is it that nearly every Muslim on the planet lives in harmony with their neighbors? This would be impossible if Islam taught violence as a religious duty.
Let's put the crusades aside, what about the European conquistadors and explorers establishing new territories and "Christianizing" the native populations in North and South America, the Caribbean, Africa, Southeast Asia, and the Pacific Islands. The United States and Manifest Destiny all of which resulted in mass atrocities such as rape, torture, slavery, mass murders, and the deaths of millions?
Christianity was spread by the sword in just about every corner of the globe. This is a historical fact that can't be denied. In fact, when we try to defend our bloody past by saying those responsible were not Christian or that they weren't following what Christianity teaches, it makes us look silly. If you say these explorers and crews that followed them into new lands didn't represent the teachings of Christ and are therefore not Christian, then you have to also apply this same method of judgment to Islamic terrorist groups since the vast majority of Muslims in the world do not adhere to or support the ideology of extremist.
The Bible teaches when we judge others our judgment must be in righteousness. It also teaches against hypocritical judgement.