Complex sentence: From about the 9th century onwards Tibeto-Burman tribes moved south from the hills east of Tibet into the Irrawaddy plain, founding their capital at Pagan in Upper Burma in the 10th century.
Split into simpler sentences: From about the 9th century onwards Tibeto-Burman tribes moved south from the hills east of Tibet into the Irrawaddy plain. They founded their capital at Pagan in Upper Burma in the 10th century.