Complex sentence: The Christian kingdoms of Nubia were the first to experience Arab incursion starting in the 7th century, though they held out through the Middle Ages until the Kingdom of Makuria and Old Dongola both collapsed in the early 14th century.
Split into simpler sentences: The Christian kingdoms of Nubia were the first to experience Arab incursion starting in the 7th century. They held out through the Middle Ages until the Kingdom of Makuria and Old Dongola both collapsed in the early 14th century.