Meanwhile, the sultan began unifying Anatolia under his rule. Forcible expansion into Muslim territories could have endangered the Ottoman relationship with the gazis, who were an important source of warriors for this ruling house on the European frontier. Thus Bayezid began the practice of first securing "fatwa"s, or legal rulings from Islamic scholars, to justify wars against these Muslim states. However, Bayezid suspected the loyalty of his Muslim Turkoman followers, so he relied heavily on his Serbian and Byzantine vassal troops in these conquests.