In the 21st century, the transatlantic bargain that has framed the relationship between the United Statates and its NATO allies is under more scrutiny than ever before. In a changed geopolitical environment, one characterized by the complexity of modern military operations, the growing power of China, and a climate of economic austerity in the West, a consensus has emerged on both sides of the Atlantic as to the need for a revised bargain to accommodate the changing dynamics of global politics. Washington is becoming less and less willing to tolerate what it sees as fundamental gaps within the Alliance-in defense spending, capabilities, and military transformation-and is sending clear signals to its European allies, as well as NATO partners, that they must take on a greater share of Alliance burdens, accelerate efforts to generate capabilities and resources, and move away from a deeply-entrenched culture of dependency. European allies are learning they must approach transatlantic relations...