Complex sentence: Kosovo, a province inhabited predominantly by ethnic Albanians, was of great historical and cultural significance to Serbs, who had formed a majority there before the mid- 19th century, but by 1990 represented only about 10 percent of the population.
Split into simpler sentences: Kosovo, a province inhabited predominantly by ethnic Albanians, was of great historical and cultural significance to Serbs. Prior to the mid- 19th century they had formed a majority in the province, but by 1990 represented only about 10 percent of the population.