The real lesson is that christianity endured 300 years of this aggression, before Pope Urban made christianity do an about turn, and began the (very minimal) Crusades against islam. They were a failure, and islamic violence against European christendom continued until the Siege of Vienna (when Jan Sobieski defeated the muslim army on September 11, 1683).
Watch just 1 minute of this video to see what happened: http://www.youtube.com/watch?feature=player_detailpage&v...
The muslim attack against Europe continued beyond this. The white slave trade continued for hundreds of years (it was stopped by a joint British/US naval bombardment of Algeria in 1815). In 1951 the UN report on slavery calculated that 5% of the population of Saudi Arabia and Yemen were still slaves.
Buddhism did not respond in the same way as christianity to islamic aggression. Many experts on the history of buddhism say that buddhism died about 1000 years ago (e.g. Conze). And they explicitly attribute this death of buddhism to the onslaught of the islamic invasion & destruction in India.
The real lesson is that some religions are actually militant political movements wrapped up in religion. Islam is one such religion. Islamic militancy was going on for hundreds of years before christianity responded in kind.