No one can say for sure what an islamist victory would have brought to Europe and the rest of the world. However, we see clearly how Christians are treated in islamic countries today, we witness the implications of "islamic law" in those lands, and we read about the growing islamic unrest in Europe. Theses hints of what could have been gives one a cold shudder, followed by a prayer of thanksgiving for those Christian warriors of long ago.
Lest we be complacent today, heed the words of Robert McMullen:
Many Christian knights, soldiers, and sailors have died defending Christendom against the onslaughts of Islam down through the centuries. Today, the borders of many European countries, Canada, and the United States are practically wide open, and the old enemy is invited to come in and make himself at home. And many 'Christians' in the West are just too busy enjoying their material prosperity to be bothered with unpleasant history.
But the enemy has not forgotten history. He remembers it all too well, and he is still deadly serious about his religion. His goal over the years has not changed in the slightest, and he is very patient. The enemy within is now smiling, just biding his time.