I used to play the game "Age of Empires" years back. In one of the episodes, you get to play Saladin, a general who fought the Crusaders. As you play the game (you are controlling the Persians), you see peasants crying "The Crusaders are attacking our caravans" and "The Crusaders are attacking our trade routes".
Few of us today have studied the historical facts of the Crusades. History tells us that Saladin won the war he was involved in with the Crusaders. It turns out that most of the Crusades after the First failed to achieve their objective - to free Jerusalem from the Muslims and making it available to Christian pilgrims.
Brief Background of the Crusades
Mohamed founded the Muslim religion by preaching about the one God, Allah. He claimed divine revelation from the angel Gabriel. After his death in 632, there was disagreement about succession. The Shia and Sunni divisions we have till today are based on two lines of succession - Ali, nephew of Mohamed and Abr Bakr, one of his closest disciples.
Military conquest expanded Muslim influence. They took Jerusalem in 638 A.D. By 700 they had North Africa and Middle East. Then, they took modern day Turkey. What was then Nicaea is now called Istanbul. So they covered areas all around the Mediterranean, entering Spain and the Iberian Peninsula in 711. By 846, a Muslim raiding party sacked St Pauls outside the walls and St Peter's Basilica. So there was a century long conquest without response.
In 1009 A.D, the church of the Holy Sepulchre, considered the holy shrine, where Jesus is believed to have been buried, was destroyed completely. It was not until 1095, that the First Crusade was dispatched to recapture Jerusalem.
Meet the Crusaders
Leaders all over Europe unanimously agreed that they needed to free Jerusalem for pilgrims to the Holy Land. People from all over Europe gathered and went East via Constantinople fighting different armies on their way to Jerusalem. The Holy City was captured by 1099.
Military historians agree that if the Crusaders went further, they could have dealt a blow to the communication center of the Muslim world and prevented them from recuperating, ensuring holding Jerusalem for long. But their objective was to make it possible for pilgrims to visit they holy places in Jerusalem, so they stopped there. Successive Crusades hardly achieved their desired goals. Saladin successfully defended Jerusalem and sent back the armies from Europe.
The Muslims expanded further in the centuries after the First Crusade, capturing Bulgaria and Serbia by 1390. Constantinople was next, captured in 1453. In 1492 they were beaten back from Spain, but they advanced from the Eastern side of Europe. After the lands around Black Sea, their land and sea assault challenged many lands. Their pirates sacked towns in Great Britain and Iceland about 1500. They laid Vienna to siege in 1529. In 1571 in the there was a great naval battle of Lepanto near Italy, where a a fleet of hundreds of ships fought on either side. Eventually, the Holy League defeated the Ottoman Turks, bringing lasting security.
Regensberg Speech - Pope Benedict XVI
The history of military conflict goes on, but the above summary of history between the 7th and 16th centuries, suffices for our context - the conversation quoted by Pope Benedict XVI in his speech at Regensberg, Germany. The Pope quoted a conversation between the Byzantine emperor and an educated Persian. The emperor spoke about a verse in the Koran, sura 2:256. He spoke about the differences between Christianity and Islam.
During those days, the language was more brusque than it is today. The emperor spoke with the background of the violent history of Islam and said that violence is not needed to spread religion. At Regensberg, Pope Benedict XVII was speaking about this conversation in an academic setting. The intent was not to attack Muslims by any means. However, the media quoted what the Byzantine emperor said as if the Pope himself said it. Put plainly, it is an instance of something taken right out of context. This is the cause for misinterpretation that we know, leading to much violence.