Complex sentence: Islam was first brought to the Balkans by the Ottomans in the mid-to-late 15th century who gained control of most of Bosnia in 1463, and seized Herzegovina in the 1480s.
Split into simpler sentences: Islam was first brought to the Balkans by the Ottomans in the mid-to-late 15th century. Turks gained control of most of Bosnia in 1463, and seized Herzegovina in the 1480s.