The Ottoman Empire declined only in the late 18th century. For most of Islam's history, it was on the offensive against Europe. It occupied Spain for 700 years and just as Spain liberated itself it invaded and conquered the Balkans. They chaffed under Ottoman tyranny for hundreds of years until the Russians liberated them in 1877-78.

Europe in contrast held territories in the Islamic middle east only sparsely. They held some enclaves in the Levant during the crusading era and occupied the middle east for a few decades following WW1.

Take this as Islams' virility or Christianity's weakness but Islam has been quite the potent force against Europe.