Japan's occupation of Southeast Asia in early 1942 cut off more than 90 percent of the global rubber supply to the World War II Allies. Without an adequate supply of this strategic material to meet military-industrial requirements, it was impossible to win the war. The Roosevelt Administration concluded that the success of the Allied war effort could depend on increasing the productivity of rubber tappers who extracted latex from rubber trees dispersed throughout Amazonian rainforests.

In response to Roosevelt's appeal, Brazil's President, Getúlio Vargas, organized a "Battle for Rubber" to increase rubber production in the Amazon. The authoritarian Brazilian government recruited around 30,000 "rubber soldiers," mainly from the arid Northeast, and sent them to work on Amazonian rubber estates.

This study explores the dynamics of global, national, and regional actors as they converged and interacted with Amazonian society in the Battle for Rubber. Migrant rubber tappers, Amazonian rubber elites, indigenous groups, North American technical advisers, Brazilian government agencies, and the Roosevelt Administration were linked in a wartime enterprise to increase rubber production.

Although the Battle for Rubber produced only modest increases in rubber production, I argue that wartime intervention by the Brazilian state in the Amazonian economy was a catalyst for significant transformations in the region, beginning in World War II and continuing into the post-war era. The Brazilian government strengthened its role in the region's economy and extended its authority into the vast Amazonian hinterlands. United States government financing for labor recruitment, rubber estates, public health programs, and transportation infrastructure for the Battle for Rubber advanced Brazil's long-term goals of integrating the Amazonian frontier into the nation.

Thousands of rubber soldiers died of malnourishment and disease in the rainforests during the Battle for rubber. Rubber soldiers who married Amazonian women had the highest chances of survival, learning from them how to adapt to an unfamiliar environment and integrate into local society. Amazonian elites successfully contested efforts by the Brazilian and United States governments to break their stranglehold over the rubber trade. Frontier indigenous societies adopted diverse strategies to survive yet another onslaught of "civilization" on their traditional lands.