The Franco-Lao Treaty of 1953 created a sovereign, independent Laos, but failed to settle the issue of who would rule the country. Consequently the years which followed were marked by increasingly bitter rivalry between the neutralists under Prince Souvanna Phouma, the right wing under Prince Boun Oum of Champassak, and the left-wing, Vietnamese-backed Lao Patriotic Front (now known under the name Pathet Lao) under Prince Souphannouvong and future Prime Minister Kaysone Phomvihane.
During this period a number of unsuccessful attempts were made to establish coalition governments. A Government of National Unity was established in 1958 under Prince Souvanna Phouma, but this fell just a few months later. Then in 1960, amidst coups and counter-coups, fighting broke out between the Royal Lao Army and the Pathet Lao. A second Provisional Government of National Unity formed by Prince Souvanna Phouma in 1962 met the same fate as its predecessor, and thereafter the situation steadily deteriorated as the conflict in Laos increasingly became a focus for superpower rivalry.
Alarmed by the growing power and influence of the Viet Minh and fearing the so-called 'domino effect', the United States began in 1953 to dispense large quantities of aid to Laos, engendering in the process widespread corruption within the Royal Lao Government. American involvement increased further in the early 1960s when – in response to a perceived Soviet-backed communist attempt to take over Laos, and in direct contravention of the 1963 Geneva agreement (which among other things banned the use of foreign troops on Lao soil) – the US government launched a covert war in Laos. At the outset this involved indirect military support, including the training and supply of RLG General Vang Paos forces in Xieng Khouang Province by US Special Forces teams and the ferrying of men and equipment into Laos from Thailand by the CIAs commercial airline, Air America. But in 1964 the Royal Lao Government gave the USA the green light to work independently, and in the following year, as the war in neighbouring Viet Nam began to escalate, American bombers began attacking the Ho Chi Minh Trail in southern Laos. By 1968, as Pathet Lao and Viet Minh forces began to get the upper hand in the north east of the country, Xieng Khouang Province became a 'free fire zone' and bombing of the Ho Chi Minh Trail increased in intensity. By the time the US bombing ended in 1973 over two million tonnes of ordnance had been dropped on Laos – including tens of thousands of bombs jettisoned on Xieng Khouang Province by B-52 crews returning to Thailand after abortive raids on Ha Noi. Thus was Laos assured the dubious distinction of being the most heavily bombed nation, on a per capita basis, in the history of warfare.
A ceasefire was finally agreed in February 1973 following the Paris Agreements between Washington and Ha Noi, and in April 1974 yet another Provincial Government of National Unity was established, once more with Prince Souvanna Phouma as Prime Minister. However, by this time Pathet Lao forces controlled large areas of the country, and following the fall of Sai Gon in April 1975 they advanced on the capital. In December 1975 King Sisavangvathana abdicated and the People's Democratic Republic of Laos was established with Prince Souphannavong as President and Kaysone Phomvihane as Prime Minister and Secretary General of the Lao People's Revolutionary Party (LPRP).