Complex sentence: By the beginning of May, however, it was clear that the Ottomans would attack Albania because of the approach of Mehmed's troops towards Albania after the end of his campaigns in Wallachia, Karaman, and the Morea.
Split into simpler sentences: By the beginning of May, however, it was clear that the Ottomans would attack Albania. This was by the approach of Mehmed's troops towards the Albanian border after the end of his campaigns in Wallachia, Karaman, and the Morea.