It was in Cordoba, Spain, where the moslems first set about conquering Europe and spreading islam by the sword. Cordoba was the capital of the caliphate. They called Iberia "Al Andalus," as it is called by them today. After about three centuries, they were thrown back across the Strait of Gibraltar.
It is a main point of moslem doctrine that once they own a place, it's theirs forever. By calling their new place at Ground Zero "Cordoba," they are announcing their intention to create a new caliphate right here in the U.S. Europe is lost, and we are on very thin ice.