Complex sentence: The northern Igbo Kingdom of Nri, which rose around the tenth century, is credited with the foundation of much of Igboland's culture, customs, and religious practices and is also the oldest existing monarchy in present-day Nigeria.
Split into simpler sentences: The northern Igbo Kingdom of Nri, which rose around the tenth century, is credited with the foundation of much of Igboland's culture, customs, and religious practices. It is the oldest existing monarchy in present-day Nigeria.