The conflict fell into three broad phases. During the initial phase following the fall of France in 1940 and the establishment of Japanese bases in France's Far Eastern colonial territories, Thailand opened up an air offensive along the Mekong frontier, attacking Vientiane, Sisophon, and Battambang with relative impunity. In early January 1941, the Thai Army launched a land offensive, swiftly taking Laos whilst entering into a more challenging battle for Cambodia where the pursuit of French units there proved more difficult. At sea, however, the heavier forces of the French navy quickly achieved dominance, winning skirmishes at Ko Chang, followed by the French victory at the Battle of Ko Chang. The Japanese mediated the conflict, and a general armistice was agreed 28 January, followed by a peace treaty signed in Tokyo on 9 May, with the French being coerced by the Japanese into relinquishing their hold on the disputed territories.