The Ottoman Turks, and especially Sultans, were forward thinkers. They would not only recruit and train foreigners for their elite army, they would have diplomatic connections in surrounding countries and territories. Once an invasion occurred, many foreign nationals also were drafted into their standing army creating one of the largest in the world at the time. Of the options, I would choose C, even though the other options were somewhat valid as well, but it was their military might that made many fall.
