In Europe, the World War II broke out in 1939. As member of the Axis powers, Japan invaded Laos in 1941 with the French Vichy Government's agreement. On the other side, temporarily allied with the Japanese Empire in the «Greater Est Asia Co-Prosperity Sphere» – which back then reigned supreme on Southeast Asia – Siam Empire took advantage of France's defeat to annex Laotian territories of Champassak and Sayaboury, both located on the east bank of the Mekong River. From 1940 to 1945, the two Asian allies, as liberators involving indigenous populations and denouncing Western colonialism, encouraged rebellions. To counteract the Japan-Siamese ambitions, Admiral Jean Decoux, the « Gouverneur général d'Indochine » (General Governor of Indochina), strove to strengthen ties between Laos and France. This policy promoted a bipartisan nationalism – on the one side pro- and on the other side anti- French presence – which would fight each other, once the global conflict ended.