Complex sentence: In 1389, however, Murad himself marched westwards, perhaps intending to eventually strike against Tvrtko, forcing Bosnians and Serbians to band together against his army at the Battle of Kosovo.
Split into simpler sentences: In 1389, however, Murad himself marched westwards, perhaps intending to eventually strike against Tvrtko. This forced Bosnians and Serbians to band together against his army at the Battle of Kosovo.