Given self-rule with the new Constitution in 1947 as part of the French Union and a federation with the rest of French Indochina, the 1953 Franco-Lao Treaty finally established a sovereign, independent Laos, but did not stipulate who would rule the country. In the years that followed, three groups led by the so-called Three Princes, contended for power: the neutralists under Prince Souvanna Phouma, the right-wing party under Prince Boun Oum of Champassak, and the left-wing, North Vietnamese-backed Pathet Lao under Prince Souphanouvong and future Prime Minister Kaysone Phomvihane.