When the Japanese army captured Burma in early 1942, it moved quickly to exploit the victory. On 4 May, Japanese forces invaded Longling County in China's Yunnan Province while 54 aircraft bombed the ancient city of Baoshan. By 10 May, the border city of Tengchong had fallen. Everything west of the Salween River -- the Nu River, as the Chinese call it -- was in Japanese hands. The 71st Army of the Chinese Expeditionary Force dug in along the eastern bank and held, frustrating every Japanese attempt to push deeper into Yunnan. For two years the armies stared at each other across the gorge, the river itself serving as a front line. Meanwhile, the severed Burma Road left China dependent on an airlift that could never deliver enough. The campaign to retake the road would require an army to fight its way through dense jungle, across mountain ranges, and down river valleys from two directions simultaneously.

General Wei Lihuang of the Chinese National Army commanded the campaign. His deputy was the American general Joseph Stilwell, a man whose abrasive temperament and relentless drive earned him the nickname "Vinegar Joe." Together they coordinated forces from three nations: the Chinese Army in India, the Chinese Expeditionary Force crossing the Salween, and British and Indian divisions pushing from the west. The Americans contributed Merrill's Marauders, a long-range penetration unit that became legendary for marching through impossible terrain. On the Japanese side, commanders rotated under the pressure -- Masakazu Kawabe, then Heitaro Kimura, then Shinichi Tanaka. Allied strength ranged from 200,000 to 400,000 troops; Japan fielded between 90,000 and 150,000. The disparity in numbers meant little in jungle mountains where a single well-fortified ridge could hold for months.

The campaign unfolded as a chain of brutal engagements. It began with the Battle of Yupang in October 1943 and the fighting in the Hukawng Valley, then ground through Maingkwan and Waluban in early 1944. The siege of Myitkyina, from May to August 1944, became one of the campaign's defining struggles -- a city whose airfield the Allies desperately needed, defended by a Japanese garrison that held out for nearly three months. Simultaneously, the Chinese Expeditionary Force launched its own crossings of the Salween, smashing into Tengchong, Mount Song, and Longling in battles that stretched through the monsoon. Tengchong was the first Chinese city recaptured from Japan, taken house by house over four months. The fighting at Mount Song lasted from June through September 1944. Longling held out even longer. By winter, the momentum had shifted decisively, with battles at Mangshi, Mongyu, and Wanding carrying the campaign into 1945. In March, the forces converged at Muse on the Burma border.

The Allies suffered more than 80,000 casualties to reopen the Burma Road and reclaim all territory west of the Salween. They claimed to have killed over 30,000 Japanese soldiers. In June 1945, the Nationalist Government awarded the Flying Tiger Flag to eleven units for their service -- the New 22nd Division for Maingkwan, Kamaing, and Hsipaw; the New 38th Division for Yupang, Mogaung, Bhamo, and Lashio; the 54th Corps for Mount Song and Tengchong. The supply line that these soldiers died to reopen functioned for only a few months before the war ended. Whether the campaign's staggering cost was justified remains debated. What is not debated is the endurance of the soldiers who fought it -- Chinese, American, British, and Indian -- through malaria, monsoons, and mountains that seemed designed to break the human body.