After languishing for five decades as a region of only marginal importance to the United States, South Asia became a major area of interest for U.S. defense planners after 9/11. The cause of this turnabout was a need for cooperation with India and Pakistan during Operation Enduring Freedom. But several subsequent developments, some quite disturbing, ensure that South Asia will remain critical for years to come. They include the presence of the Taliban and al Qaeda militants in Pakistan and possibly Kashmir, anti-American and anti-national terrorism in both nations, turmoil in the disputed state of Kashmir, and a potential for nuclear conflict between India and Pakistan. On a more positive note, Washington has improved its political and military relationships with New Delhi and Islamabad, which has raised expectations. Because of rivalry between India and Pakistan, which began with their independence from Britain in 1947, the United States has never been able to maintain close relations with both nations simultaneously. India drifted between nonalignment and an outright alliance with the Soviet Union, while Pakistan was a staunch American ally in the fight against communist expansion. When the United moved closer to India after the Sino-Indian conflict in 1962, and again during the 1990s following the breakup of the Soviet empire, its relations with Pakistan waned. Today the challenge is translating increased influence in both New Delhi and Islamabad into tangible results in the war on terrorism, stabilizing Indo-Pakistani competition, and promoting other American interests throughout the region. This article discusses Operation Enduring Freedom and its effect on Pakistani-American relations, Indo-American cooperation after 9/11, terrorism in South Asia, military tension between India and Pakistan, and the danger of nuclear war between the two countries. (2 tables, 1 map, 6 photographs).