After being crushed in the Crusades. The Muslim empire never kept up with Western Civilization in any way. Islam can never fight the Jihad they did in the 8th century. So they use “Terror” as a Military Strategy. They could never have imagined that the West would commit cultural suicide via political correctness.
Islam is incompatible with liberty and Western civilization. The tenants of Islam lead to the death of art, innovation, liberty and technology. Islam is a malignant, metastasizing cancer on civilization. The best thing to do with cancer is remove it!
The muslims crushed the Crusaders not the other way around. It was some 500 years later that the muslim hordes were stopped in Kosovo, Spain and France.
Muslims never kept up because their ‘religion’ does not permit any advances past the 7th century.
Islam is currently in revival mode advancing by hiraj (peaceful jihad by invasion) into Europe (one million in the past year), while ISIS is following the traditional jihad path - all perceptions will change as soon as they acquire (buy) nuclear weapons - just a matter of time. The last time around it only took Mohammad and his Disciples 100 years to go from Medina to Mauritania to Tehran to Barcelona, crushing classical western civilization and Christianity. Today, we still cringe before their onslaught aka PC diversity, failing to understand the women and boys sold into slavery today are a prelude of what is to come - slave markets were very big and in fact the only profitable business during the time 628-1450 AD.
Never underestimate your enemy ...