Complex sentence: After the Axis' invasion of Yugoslavia in April 1941, territories of Yugoslavia with substantial Albanian population were annexed to Albania: most of Kosovo, as well as Western Macedonia, the town of Tutin in Central Serbia and a strip of Eastern Montenegro.
Split into simpler sentences: After the Axis invasion of Yugoslavia in April 1941, territories of Yugoslavia with substantial Albanian population were annexed to Albania. Albania annexed most of Kosovo, as well as Western Macedonia, the town of Tutin in Central Serbia and a strip of Eastern Montenegro.