The people of Laos are ethnically diverse, though a truly authoritative survey of all ethnic groups has never been conducted. Before the wars in the '60s and '70s, more than 60 different groups were commonly identified. The 1985 census listed 47 groups. Some of these were made up of only a few hundred people. A lot of this huge variation in estimated numbers was a result of disagreement about what actually represents a separate ethnic group. The 1985 census also defined three general ethnic group classifications defined by origin and language. Defining ethnicity in Laos still remains an inexact science.

The lowland Lao, or Lao Loum, make up the majority of the population, 66% in total. In turn they are made up of a number of different sub groups. All Lao Loum speak languages of the Tai-Kadai family; Lao, Lue, Tai Dam (Black Tai), and Tai Deng (Red Tai). They stay in the river valleys and engage in wet rice cultivation. The distinction between Thai and Laos is a political one rather than an ethnic one. The vast majority of people who could be classified as Lao actually live in the northeastern provinces of Thailand.

The Lao Theung, or midland Lao, account for about 24% of the population of Laos; they were originally displaced to higher ground by the migrations of the Lao Loum. The cultural and linguistic variation among the numerous Lao Theung groups is more pronounced than those of the Lao Loum or Lao Sung, or upland Lao. Groups range from the Khmu and Lamet in the north, to the Katang and Makong in the center of the country, to the Loven and Lawae farther south.

The Lao Sung, often called hill tribes, make up about 10% of the population. These groups are Miao-Yao or Tibeto-Burmese speaking peoples who migrated relatively recently from Southern China. In Laos most highland groups live on the upper slopes of mountains in the north farming rice on steeply stepped terraces. Some of these groups have been resettled in lowland areas since the 1970s. The Hmong are the most numerous of these hill tribe groups, with villages spread across all the Northern provinces. Mien (Yao), Akha, Lahu, and other related groups are fewer in number and tend to be located in more restricted areas.

There have been some tensions along ethnic lines although this is more an issue of political vendetta than genuine racial friction. Over a millennia lowland Tai-Lao migrants pressured the Lao Theung groups forcing them to move to higher ground. They also dominated them politically. The Lao Theung were frequently referred to as Kha, a derogatory term meaning "slave" since they were historically often forced into being indentured labor.

French colonial rule tended to favor lowland Lao by granting them access to education and putting them in a position of authority. In the early 1900s, Lao Theung and Lao Sung groups mounted several insurgencies against the French and the Lao-Thai. The rebellions were easily suppressed, but the tensions lived on. During the 1950s, significant numbers of Lao Theung and Lao Sung fought for the Pathet Lao. After 1975, the number of Lao Theung and Lao Sung in positions of government and social responsibility increased, but even in the 1990s they were still underrepresented.

The unresolved issue of Hmong resistance to Communist rule persists. There were about 30,000 Hmong recruited by the CIA to fight against the Pathet Lao and North Vietnamese in during the '60s and '70s. When the Americans left, remnants of this force (with their families) remained stranded in the jungle and carried on the war. There is a continuing refugee problem for Thailand, Laos, and the U.S. Some would say that for the situation not to be solved suits certain political vested interests. In 2003 Bangkok-based Australian photographer Philip Blenkinsop was the first foreigner to find these beleaguered groups. Their situation was one of intense distress.

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