Forged in the wake of World War II, the U.S.-Japan security alliance has served as one of the region's most important military relationships and as an anchor of the U.S. security role in Asia. Revised in 1960, the Treaty of Mutual Cooperation and Security grants the United States the right to military bases on the archipelago in exchange for a U.S. pledge to defend Japan in the event of an attack. The partnership has endured several geopolitical transitions, rooting its framework in the postwar security environment and expanding in the aftermath of the Cold War with the rise of China and a nuclearizing North Korea. Cooperation during the Gulf and Iraq wars and the March 2011 Tohoku earthquake reaffirmed the strength of the alliance, but challenges remain. The U.S. military presence on Okinawa, North Korea's nuclearization, territorial disputes with China, and Japan's recent push to upgrade its defense preparedness have all challenged the alliance's resilience as the Obama administration considers the direction of its strategic pivot to the Asia-Pacific region.