The Lao People's Democratic Republic (Lao PDR) is the least populous country in the Indochina Peninsula. The 1995 census recorded a population of 4,575,000, which is just under half that of Cambodia (9.8 million), and between 10-6% of that of Myanmar (46.5 million), Thailand (59.4 million) and Vietnam (75.5 million). Its total area of 236,800 km2 makes it the second-smallest country, between Cambodia (181,000 km2) and Vietnam (330,400 km2), and a long way behind Thailand (513,100 km2) and Myanmar (676,600 km2). Like Myanmar and Thailand, Laos is located in a river basin. However, unlike the basin in those countries, the Mekong Basin is shared by six countries, with Laos occupying 26%, China and Myanmar 22% together, Thailand 23%, Cambodia 20%  and Vietnam 9%.

A multi-ethnic state with a territory off-center  from the Mekong

 The dominant ethnic group accounts for a much smaller  proportion of the population in Laos than in the  neighboring countries. In the 1995 census, the Lao made up only 52% of the population. With the other  related ethnic groups, the Tai-Kadai ethnolinguistic  family constitutes two-thirds of the population, which is  slightly less than the 69% generally attributed to the  Burmans in yanmar. This is far below the domination  of the Tai-Kadai family in Thailand (estimated at 83%),  the  Mon-Khmer  in  Cambodia  (87%)  and  the  Vietnamese/Kinh in Vietnam (87% in the 1989 census). Each of these dominant ethnic groups created its own  state after a "march south". The Lao, following the  Mekong, settled in the valleys of the river and its  tributaries, where they practiced wet rice cultivation,  pushing the Austro-Asiatic indigenous people towards  the slopes, whence they derived their respective names of  Lao Loum (Lao of the lowlands) and Lao Theung (Lao of  the slopes).  This fragmented river space and pronounced multi-ethnic structure can be explained by the relatively late timing of the Lao's "march south". The capital of the kingdom ofLan Xang was moved from Luangphrabang to Vientiane in 1553, and the southward movement halted there. The Thai shifted their capital from Chieng Mai to Sukothai and reached Ayuthaya, at the head of the Chao Praya delta, in 1350. They took over the declining Khmer empire in 1431 and blocked the Lao's access to the Mekong Delta. Deprived of a delta base for rice cultivation and of access to international maritime trade essential for building a nation of size, the Lao were unable to rival their neighbours (Christian Taillard, 1989).  The unequal balance of power with the kingdom of Siam manifested itself in the 19th century with the loss of the territories on the right bank of the Mekong, which today make up north-eastern Thailand and which include the broadest plains of the middle river basin. And twice in  half a century—in 1778 and 1828—the Lao peoples of the  left bank were deported to the Siamese bank. As a result,  the Lao in Lan Na, the former kingdom of northern Thailand, and in Isan in the north-east, estimated at  respectively 30% and 20% of the population of Thailand,  are nine times more numerous than the 2.4 million Lao in  Lao PDR. The arrival of new waves of Miao-Yao and  Tibeto-Burman immigrants in the 19th century further  reduced the proportion of Lao. The latter groups settled on  the mountain peaks, whence the term Lao Soung (Lao of  the summits) used to designate them. 

        The nation's history explains why Laos is currently the most mountainous and most ethnically diverse country  in the peninsula and why its territory is off center in  relation to the Mekong. The width from east to west attains  500 km in the north of Lao PDR, but is only 150 km at  Thakhek in the Center, accentuating the effects of  meridian elongation (1,835 km by road and 1,865 km  along the Mekong) and hampering territorial integration.