The Crusades were religious wars

The short answer is yes. They were called the Holy Crusades in their time and people were called to battle from the pulpits of churches. People who went to fight were absolved of all former sins and were considered soldiers of the Church and were thought to be fighting for Jesus, God and "to free the Holy Land from Mohammedan tyranny."

There were many different Crusades mounted between 1075 - 1292. When people speak of the Crusades they are generally talking about the wars in Palestine and the attempt to drive the Muslim Arabs out of Palestine, which had previously been held by the Eastern Orthodox Byzantine Empire. The justification was to free the "Holy Land" from non-Christian rule and this is why most soldiers got involved. Certainly there was a lot of religious turmoil at the time. The Crusades were also mounted against Jews, pagans, traditionally non-Christian ethnic groups, political enemies of the Vatican and even Orthodox Christians. So, there was some non-religious fighting going on within the Crusades. But, over all the Crusades were based on the idea that the Catholic European Christians were the only people that God wanted in charge of the "Holy Land" and they threw generations of people into a basically unwinnable battle for the glory of God.

yes, that lasted over 100 years usually used in the Dark Ages