Complex sentence: In the 7th century an independent Muslim state emerged in the archipleago, but it was subsequently conquered by Yemen, then intermittently by the Kingdom of Medri Bahri (Land of the Sea).
Split into simpler sentences: In the 7th century an independent Muslim state emerged in the archipleago. However, it was subsequently conquered by Yemen, then intermittently by the Kingdom of Medri Bahri (Land of the Sea).