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In American history, the major milestones of the U.
S. foreign policy often reflected deeper changes in the relation of the United States towards Europe, more specifically they reflected an evolution in the transatlantic balance of power. The main long-term change for U.S. global standing occurred throughout the Second World War: the transatlantic relation, in its contemporary understanding, borne out of the institutional order linking the United States to many European countries, also emerged during that era with the creation of NATO in 1949 – a military organization created to address the Soviet threat. This simple fact is worth remembering as it explains why, despite multiple internal crises throughout the four decades of its existence, the challenges NATO has faced since the end of the cold war are more profound. Although NATO has had ups and downs, it now faces a major crisis of unprecedented scope as evidenced by the ways U.S. President Donald J. Trump has characterized the organization as “obsolete”. The main challenge today relates to two enduring issues: U.S. reluctance to comply with the constraints of an alliance such as NATO (in particular due to the provisions of Article 5) and divisions among European countries. In fact, both issues have been exacerbating each other since the end of the cold war. In this context, the current crisis in the transatlantic relationship is of grave concern due to the fact that the American president drives its escalation, through his open skepticism on the value of NATO but also his rhetorical attacks aiming at the European Union and its member states. Moreover, the crisis is worrisome as it evolves while NATO and the European Union both face simultaneous institutional crises.

In light of the growing importance of Asia-Pacific in the American strategic debate, this article seeks to shed light on the main patterns of continuity and change between the Obama and Trump administrations' policies in the region and, in particular, vis-à-vis China's rise. To do so, it proposes a structured comparison of the main components of U.S. defense policy in the Asia-Pacific under the two presidencies: their threat perceptions of China; the ensuing policy objectives; and the ways in which these objectives shaped the (re) definition of U.S. regional alliances and defense cooperation agreements as well as the military-technological capabilities deployed in the Asia-Pacific. To that end, the article draws on a wide range of primary sources including seventy-five semi-structured interviews with senior U.S. officials. What emerges from this analysis is that, beyond electoral slogans and the vagaries of “twitter diplomacy”, the Trump administration's defense policy in the Asia-Pacific is part of a long-term cumulative evolution rather than a radical departure from previous policies.

As soon as he became President, Donald Trump tasked the U.
S. Department of Defense to conduct a review of the nuclear posture. While the Obama Administration had initially laid ambitious plans in favor of nuclear disarmament, from 2014 on it ended up strengthening the U.S. deterrence posture and modernizing the nuclear forces as tensions increased with Russia, China and North Korea. Despite Donald Trump's initial statements, the 2018 Nuclear Posture Review reflects more continuity than change, while preparing U.S. deterrence policy for an era of renewed strategic competition between great powers. These new doctrinal orientations not only reaffirm the role of nuclear weapons in U.S. strategy, but embrace again the view that military superiority is the main way to ensure U.S. national security.

Irregular warfare is a form of conflict that keeps haunting the United States' grand strategy and defense policy in spite of its efforts to avoid it. The 9/11 attacks and subsequent military operations in Afghanistan, Iraq and elsewhere opened a new “irregular cycle”. It witnessed a renewal of counter-insurgency doctrine – abandoned since the Vietnam War – that reached its highpoint at the end of the second term of George W. Bush. The arrival of Barak Obama inaugurated an ebb in irregular warfare, attested by the attempt to withdraw from Iraq and Afghanistan, and to build up partner capacity, deemed more fit to deal with these complex conflicts. However, this security architecture canvas collapsed, shaken by the Arab Spring uprisings, the jihadi renewal and the “hybrid” strategies of Russia, China and Iran. To these challenges, the Trump administration's answer balanced between a pulling out rhetoric and an actual policy of doubling down.

The strategic culture of the United States, deeply influenced by Jomini more than by any other theoretician, has led it to develop a specific vision of the “principles of war”, revealing its singular approach to operations and the use of force in international relations. In December 1921, Americans adopted in TR 10-5 a first official list of nine principles: Objective, Economy of Forces, Offensive, Maneuver, Unity of Command, Security, Mass, Surprise and Simplicity. Those principles were enthusiastically adopted, probably because such a standardized list fell in line with a scientific management of operations. Subsequently, from the Cold War era to the last operations in Afghanistan, this approach was criticized and questioned by influential civilian strategists and US officers. Yet, in a century, the list was paradoxically never changed. Returning to these debates, from 1918 to today, this article offers a rereading of this paradox, by examining the strategic culture of the United States, and a doctrinal legacy with which the US military is preparing to face the operational challenges of an uncertain twenty-first century.