Complex sentence: Historical mention of the Shan states inside the present-day boundaries of Burma began during period of the Pagan Dynasty and the first major Shan State of that era was founded in 1215 at Mogaung, followed by Mone in 1223.
Split into simpler sentences: Historical mention of the Shan states inside the present-day boundaries of Burma began during period of the Pagan Dynasty. The first major Shan State was founded in 1215 at Mogaung, followed by Mone in 1223.