Complex sentence: Boba's views were rejected by most specialists but were further developed in the 1990s by Charles Bowlus, who writes that Moravia emerged in the region of the "confluences of the Drava, Sava, Drina, Tisza, and southern Morava rivers with the Danube".
Split into simpler sentences: Boba's views, which were rejected by most specialists, were further developed in the 1990s by Charles Bowlus. He writes that Moravia emerged in the region of the "confluences of the Drava, Sava, Drina, Tisza, and southern Morava rivers with the Danube".