In the early 1960s, the U.S. Central Intelligence Agency (CIA) began to recruit the indigenous Hmong people in Laos to join fighting the Vietnam War, named as a Special Guerrilla Unit led by General Vang Pao. About 60% of the Hmong men in Laos were recruited by the CIA to join fighting for the "Secret War" in Laos. The CIA used the Special Guerrilla Unit as the counter attack unit to block the Ho Chi Minh Trail, the main military supply route from the north to the south. Hmong soldiers put their lives at risk in the frontline fighting for the United States to block the supply line and to rescue downed American pilots. As a result, the Hmong suffered a very high casualty rate; more than 40,000 Hmong were killed in the frontline, countless men were missing in action, thousands more were injured and disabled.
General Vang Pao led the Region II (MR2) defense against NVA incursion from his headquarters in Long Cheng, also known as Lima Site 20 Alternate (LS 20A). At the height of its activity, Long Cheng became the second largest city in Laos. Long Cheng was a micro-nation operational site with its own bank, airport, school system, officials, and many other facilities and services in addition to its military units. Before the end of the Secret War, Long Cheng would fall in and out of General Vang Pao's control.
The Secret War began around the time that the U.S. became officially involved in the Vietnam War. Following the U.S. withdrawal from Vietnam in 1975, the Lao kingdom was overthrown by the communists and the Hmong people became targets of retaliation and persecution. While some Hmong people returned to their villages and attempted to resume life under the new regime, thousands more made the trek to and across the Mekong River into Thailand, often under attack. This marked the beginning of a mass exodus of Hmong people from Laos. Those who did make it to Thailand generally were held in squalid United Nations refugee camps. Nearly 20 years later, in the 1990s, a major international debate ensued over whether the Hmong should be returned to Laos, where opponents of their return argued they were being subjected to persecution, or afforded the right to immigrate to the U.S. and other Western nations.