In 1913, on the eve of World War I, the United States featured a State Department of some 213 employees in Washington, dc—manual labourers included—and an Army that was barely a fifth the size of Bulgaria’s. The Navy was another matter, but, however impressive, it lagged behind both Britain and Germany in technology and size. Thirty years later, the United States was well on its way to becoming the globalized military and political power it would be when Harry Truman left office in 1953 and that we know today. John Thompson’s A Sense of Power is an attempt to understand that great transformation from the unusual premise that it may not have been necessary.

The question, of course, is what one means by ‘necessary’. Thompson conforms to recent political parlance in seeing necessity as the opposite of choice—as in ‘wars of necessity, wars of choice’, though he himself does not invoke that well-known formula. As I write, the polarity of necessity and choice has been given unexpected relevance by a president-elect who says that many of the us engagements in the world are unnecessary and certainly bad choices from the national standpoint of ‘America’. It is a language that rejects, it seems, the basic frame in place since the 1940s, whereby the United States is ultimately responsible for world order—responsible for the whole. A Sense of Power is about the emergence of that conception in the first half of the twentieth century, more particularly about the policymaking debates and choices that created it as seen in relation to a certain set of actually existing necessities. A historian of the us at Cambridge, Thompson brings to the subject a lifetime’s study of these debates, focused above all on the Progressive era.

This, then, is a study of decisions in cases where, all things being equal, the possibilities run from the widest range of options to no choice at all. ‘Necessity’, on Thompson’s view, impinges on policymaking in two ways: ‘security’ and ‘economy’. Every polity must evaluate external threats and provide the resources to maintain its continuity, inside and outside; every polity must attend to the kind of economic interests inside that produce the wherewithal for population and state alike. The remainder, then, is ‘choice’. It was indeed one such policy decision, the Vietnam War, that originally moved Thompson to reflect on these problems. Clearly, no issue of ‘security’—whatever successive presidents insisted—was really at stake for the United States in Vietnam, nor any economic interests. Intervention, then, seemed a matter of choice, a bad one (Thompson implies) but a choice nonetheless. The task, accordingly, is to find out how the United States moved from the notion that virtually nothing is necessary to one in which virtually everything is. Thompson’s pitch here is that, strictly speaking, the historical shift was grounded in a mistake: necessity was a choice, so to speak. The United States was never subject to the kinds of systemic pressure that would have required the movement to globalism: hence the luxury of having the choice to make it. The question, then, is how and why it was actually made.

Security and economic interests correspond to the two main explanatory positions which do invoke systemic necessity and form A Sense of Power’s polemical counterpoints: realism on the one hand, economic determinism on the other. On empirical grounds, he thinks both are wrong, and sets out to show this by analysing the familiar shifts and pivots in us foreign relations during this transitional period: the War of 1898 and the imperial-colonial splurge that followed it; the entry into World War I in 1917 and its post-war, Wilsonian debacle; the relative retreat of the 1920s and 30s; the uneven but fairly consistent move from 1938 on towards involvement in the approaching World War II; the massive, ensuing war effort; and the final transition to full globalism in the early Cold War from 1947 onwards. This is not, Thompson underlines, a comprehensive history but an investigation of a particular thematic, and so by nature selective. Nevertheless, A Sense of Power sweeps across a great deal of territory, often in considerable, interesting detail. The reference to Vietnam indicates a problematic originating in the 1960s or 70s, when historiographic arguments were in every way sharper; Thompson is unusual in taking explanatory models more seriously than is typically the case after the cultural turn in the field.

The realist alternative centres on necessities of ‘security’, arguing variously that objective power capabilities lead inherently to the exercise of that power, that the international ‘system’ requires such exercise as inaction would mean insecurity, or that inaction would create instability in the hegemonic order of things. In due course, any gap between power and its exercise would tend to close. Historically, it is then argued, the United States did in fact come to calibrate objective power and ‘security’. Thompson agrees that the country had the means to implement a large, global policy, or at least a much more vigorously expansive one than was actually the case. The potential here was not in doubt. The United States, having already become the biggest manufacturer in the world by 1870, produced almost 40 per cent of all goods at the start of World War I. By 1945, when it had demonstrated its awesome military and economic power in another global conflagration, the figure had risen to 50 per cent; and this was a war during which domestic standards of living had actually risen. Yet, except for the two war efforts, there remained a discrepancy between what the United States could do and what it actually did. Only after 1945 did that divide close with the decisions surrounding the advent of the Cold War.

Thompson thinks this shift had nothing much to do with systemic pressure or mounting problems of security. There is, to begin with, no universal correlation between potential and actual power. Moreover, he argues, it was not the case that improving technology and spatial connectivity, central factors in the alleged security exposure, brought increasing danger. Air power, for instance, actually made naval attacks more difficult and defence easier. No invasion of North America was ever possible; Charles Lindbergh was right about that. Not until the mid-1950s did the United States face real vulnerability, and even then American deterrent power over the Soviet Union was still overwhelming. From the Wilsonian break onwards, on Thompson’s view, the public also grasped the essentials, both the power in reserve and the limited stake in exercising it: why bother? The classic antithesis here is provided by the Athenians in Thucydides, who obliterated the Melians because they had the power to do so: desisting would paradoxically be a sign of hubris. How and why did the us shift to a similar kind of chosen necessity?

Though geostrategic calculation, being about the future, is always open to speculation based on worst-case scenarios—and absence of invasion is arguably too limited a sense of ‘security’—Thompson’s account is generally persuasive. So is his critique of the economic argument, which derives external expansionism from the needs of capitalism for markets, raw materials and financial exports; or alternatively from corporate influence, or from faulty notions about said needs. Here, as Thompson demonstrates, the actual economic logic seems to unfold in a counterintuitive manner: the more the United States industrialized, the less incorporated into international capitalism it became, and the less external markets meant as well. Certain industries, to be sure, had big stakes abroad and affected policy, but as an economic system, the United States could get along very nicely in existing, largely self-sufficient conditions, with capital reproduction overwhelmingly concentrated in the domestic sphere. There is an asymmetry, so obvious as to be almost banal: the outside meant less to the us than the us meant to the outside. The financial system of the Dominican Republic—though not one of Thompson’s examples—was entirely controlled by the United States in the early 1900s, first by a private corporation in New York, then by Washington; but this condition, decisive for the Dominicans, was of little consequence for the imperial power. It was domination for economic as well as strategic reasons, but it was not ‘necessary’. The argument, nevertheless, gets more complicated in the 1920s and 30s—the absence of proper us ‘leadership’, despite ostensibly private initiatives to remedy the central problem of war debts, certainly contributed to the unprecedented crisis of the 1930s. Yet this was in retrospect. In the 1920s, one would have been hard pressed to argue that the us was not doing exceedingly well, and very much on traditional concepts. George Washington’s (and Alexander Hamilton’s) commandment—a maximum of trade, a minimum of political entanglement—never made more sense than in the post-Wilsonian interwar period.