The only country to escape colonialism in Southeast Asia, Thailand on the eve of the Second World War was a kingdom deep in the throes of militarism, led by a charismatic strongman obsessed with questions of national greatness and dreams of empire. In 1940 the Thais took advantage of France's metropolitan defeat to fulfill revanchist yearnings by demanding the return of 'lost provinces' in Laos and Cambodia that had been ceded to Indochina half a century earlier. What followed was a border war with Vichy that culminated in Japanese mediation and the territories' return. Contrary to what most histories of the Pacific War would suggest, Japanese forces landing in peninsular Thailand on their way to Singapore found themselves opposed by local garrisons, one of which held out well beyond the ceasefire that Bangkok eventually ordered. But armistice soon turned into alliance in the wake of Japanese successes of 1942, with the Thais declaring war on Britain and the United States. Driven yet again by expansionist ambitions, the Thais mounted an invasion of Burma's eastern Shan States, coming into contact with the Chinese army. A renewed offensive in January 1943 saw Thai troops reach the borders of Yunnan. The Thai army also began an occupation of northern Malaya that same year. A change of government in 1944 made possible by Axis setbacks in Europe and the Pacific brought to the fore a new government secretly controlled by an anti-Japanese resistance movement under whose direction the army devoted the final year of the war to preparing for an armed uprising that would ultimately never occur. Drawing upon a wide range of hitherto untapped sources and featuring several photographs never before published, this is the first full account of Thai ground combat operations in the Second World War to be available to an international readership. This first of two volumes covers the border war with Vichy France of 1940-41 and is accompanied by the Royal Thai Army's orders of battle up to mid-1941, as well as a detailed overview of uniforms up until 1945. The next installment will cover the army's participation in what remains locally known as the Greater East Asia War alongside chapters on weaponry and unit organisations. AUTHOR: Punyaphan Klykoom is a Bangkok-based government affairs consultant with a track record of helping multinationals surmount regulatory and public policy challenges. He has a long abiding interest in the histories and cultures of Southeast Asia and hopes to one day write about the wars of nineteenth century Siam. 130 b/w photos, 8 colour photos, 6 colour ills, 6 colour profiles, 15 tables, 4 maps