There has been only limited population movement into Laos in modern times. During the late 1960s and early 1970s, under pressure of combat operations, Black Tai tribesmen moved southward into the Mekong Valley. Between 1975–90, over 360,000 Laotians fled to Thailand and China. The majority resettled and were given new lives in Western nations. To date, more than 27,000 Laotians have repatriated. In 1996, some 6,000 Laotian refugees remained in Thailand, and several hundred remained on collective farms in China. As of 1999, about 1,100 of the small number of refugees still remaining in Ban Napho camp in Thailand were determined not to have valid refugee claims. The two governments agreed that they should return to Laos, with UNHCR assistance; however, only a few families and individuals have volunteered to do so thus far. In the mid-1990s, as Laos opened up to international investment and development, Vietnamese workers began migrating to Laos— although in relatively small numbers—to work in the construction industry, primarily. The net migration rate for 2000 was -0.3 migrants per 1,000 population. The government views the immigration level as satisfactory, but the emigration level as too high.