Turkey has been one of the staging points for that slow invasion. The border between the Christian world and the Muslim world has fluctuated but is generally considered to be between the Balkans and Turkey. That is why the American government opposes the Serbs and supports Bosnia. Bosnia is a Muslim presence in an area that has historically been Orthodox Christian. Serbia serves as the bulwark of Christendom - holding back the Arab hordes.
Turkey is the base camp of the invasion.
Political developments in Turkey as a reaction to the rise of Islamic fundamentalism will be fascinating to watch over the next years. This may be the most significant development in foreign affairs since the fall of the Soviet Union. Lest anyone misunderstand, I personally fear and loathe a growing Muslim militancy. I do not want Muslims in America or Europe. I want America to be a Christian nation again.