The most densely populated part of the country is the valley of the Ayeyarwady (Irrawaddy) River, which, with its vast delta, is one of the main rice-growing regions of the world. Mandalay, the country's second largest city, is on the Ayeyarwady in central Myanmar. The Ayeyarwady basin is inhabited by the Burmans proper, a Mongolic people who came down from Tibet by the 9th cent. and now represent nearly 70% of the mainly rural population. The valley is surrounded by a chain of mountains that stem from the E Himalayas and spread out roughly in the shape of a giant horseshoe; the ranges and river valleys of the Chindwinn (a tributary of the Ayeyarwady) and of the Sittaung and the Thanlwin, or Salween (both to the E of the Ayeyarwady), run from north to south.
In the mountains of N Myanmar (rising to more than 19,000 ft/5,790 m) and along the India-Myanmar frontier live various Mongolic peoples; the most important are the Kachins (in the Kachin State in the north) and the Chins (in the Chin State in the west). These peoples practice shifting cultivation ( taungya ) and cut teak in the forests.
Between the Bay of Bengal and the hills of the Arakan (or Rakhine) Mts. is Rakhine State, a narrow coastal plain with the port of Sittwe, which is home to the Arakanese (or Rakhine). In E Myanmar on the Shan Plateau is Shan State, home of the Shans, a Tai people closely related to the Thai who, at nearly 10% of the population, are Myanmar's largest minority. South of Shan State are the mountainous Kayah State and Kayin State; the Karens, who inhabit this region, are of Tai-Chinese origin, and many are Christians. South of Kayin State is the Tanintharyi region, a long, narrow strip of coast extending to the Isthmus of Kra. At its northern end is the port of Mawlamyine, Myanmar's third largest city.
Most of Myanmar has a tropical monsoon climate; however, N of the Bago Hills around Mandalay is the so-called Dry Zone with a rainfall of 20 to 40 in. (51–102 cm). On the Shan Plateau temperatures are moderate. Theravada Buddhism is the religion of about 90% of the population; there are Christian and Muslim minorities. Burmese (the tongue of the Burmans) is the official language, but each of Myanmar's ethnic minorities has its own language; in all, over 100 languages are spoken.