A fertile floodplain and tropical monsoon climate, ideally suited to wet-rice (tham na) cultivation, attracted settlers to this central area in preference to the marginal uplands and the highlands of the northern region or the Khorat Plateau to the northeast.

[1] By the 11th century AD, a number of loosely connected rice-growing and trading states flourished in the upper Chao Phraya Valley.

[1] They broke free from domination of the Khmer Empire, but from the middle of the 14th century gradually came under the control of the Ayutthaya Kingdom at the southern extremity of the floodplain.

[1] Successive capitals, built at various points along the river, became centers of great Thai kingdoms based on rice cultivation and foreign commerce.

[1] Unlike the neighboring Khmer and Burmese, the Thai continued to look outward across the Gulf of Thailand and the Andaman Sea toward foreign ports of trade.

[1] Together, the Chao Phraya and Mekong systems sustain Thailand's agricultural economy by supporting wet-rice cultivation and providing waterways for the transport of goods and people.

Extreme points of the mainland The National Research Council divides Thailand into six geographical regions, based on natural features including landforms and drainage, as well as human cultural patterns.

[3] They are: Although Bangkok geographically is part of the central plain, as the capital and largest city this metropolitan area may be considered in other respects a separate region.

Traditionally, these natural features made possible several different types of agriculture, including wet-rice farming in the valleys and shifting cultivation in the uplands.

The region consists mainly of the dry Khorat Plateau which in some parts is extremely flat, and a few low but rugged and rocky hills, the Phu Phan Mountains.

[1] Metropolitan Bangkok, the focal point of trade, transport, and industrial activity, is on the southern edge of the region at the head of the Gulf of Thailand and includes part of the Chao Phraya delta.

[1] North-south mountain barriers and impenetrable tropical forest caused the early isolation and separate political development of this region.

[1] International access through the Andaman Sea and the Gulf of Thailand made the south a crossroads for both Theravada Buddhism, centered at Nakhon Si Thammarat, and Islam, especially in the former Pattani Kingdom on the border with Malaysia.

[8]: 3  Southern Thailand has mild weather year-round, with less diurnal and seasonal variations in temperatures, due to maritime influences.

[8] The driest areas are the leeward sides of the central valleys and the northernmost portion of south Thailand, where mean annual rainfall is less than 1,200 mm (47 in).

[8]: 4 Pattamawadee Pochanukul, a lecturer from the Faculty of Economics at Thammasat University, estimates that about 59% of all arable land in Thailand belongs to the state.

Information from the Office of the National Anti-Corruption Commission (NACC) shows that members of the house of representatives in 2013 owned a total of 35,786 rai of land (about 57.3 km2).

[1] Most borders were stabilized and demarcated in the late 19th and early 20th centuries in accordance with treaties forced on Thailand and its neighbors by Britain and France.

[1] Adding to general border tensions were the activities of communist-led insurgents, whose operations were of paramount concern to the Thai government and its security forces for several decades.

[1] Often the real source of border problems was ordinary criminals or local merchants involved in illegal mining, logging, smuggling, and narcotics production and trade.

[1] Recently, the most notable case has been a dispute over Prasat Preah Vihear submitted to the International Court of Justice, which ruled in favor of Cambodia in 1962.

[1] During the years that the Cambodian capital, Phnom Penh, was controlled by the Khmer Rouge regime of Pol Pot (1975 to 1979), the border disputes continued.