As the 11 September 2001 attacks on the U.S. homeland and natural disasters like Hurricane Katrina revealed, the United States cannot neglect to protect and defend its citizens against disasters—whether manmade or natural—on its soil. In a globalized world, nations have been forced to redefine their concept of security, looking beyond traditional military threats to the growing threats posed by unstable political, economic and social environments. The world is smaller and flatter—as Thomas Friedman suggests —and its threats are larger and more complicated.To confront modern security challenges, the Army has adapted its operational and institutional structure, changing from threat-based to capabilities-based command structures. In this new Army structure, each regional unified combatant command will be assigned a theater army for its area of responsibility (AOR; see figure on page 2) that will also report to Headquarters, Department of the Army (HQDA). In addition to fulfilling their Title 10, U.S. Code responsibilities, theater armies will develop organic, deployable headquarters, giving the Army new capabilities and new options to act more effectively across the full spectrum of operations.This National Security Watch discusses U.S. Army North/Fifth Army (USARNORTH) and its AOR, which includes the continental United States, Alaska, Canada and Mexico.4 USARNORTH is charged with Army homeland defense and civil support operations and army-to-army theater security cooperation with Canada and Mexico in order to “protect the American people and their way of life.”