Explaining his move to rename the United States Department of Defense the Department of War, as it was known prior to 1949, President Donald Trump explained it had “a stronger sound.”It offered better messaging too. “Defense is too defensive; we want to be offensive too,” he said.The once and future Department of War would revive the spirit of the years when “we won everything.”Trump’s language — and the logic behind it — demonstrates how little America’s current leaders have learned from the clear failures of their predecessors across 70 years. American policies after the Second World War achieved great things: substantially aiding the reconstruction of devastated Europe and Japan, for instance, while spearheading the building of an integrated global economy that fostered unparalleled growth. There were also grave flaws in American designs and actions, of course, though they rarely if ever stemmed from a lack of aggressive assertiveness and an appetite for winning. Trump’s failure to diagnose the real roots of real problems portends a worsening of already terrible costs and consequences.Perpetual preparednessA key source of Trump’s weaknesses is his shallow or distorted grasp of history. His failure here is understanding that the Department of Defense saw “offence” thoroughly embedded into its conception of defence.Think “the best defence is a good offence” on steroids. George Kennan’s famous “containment policy,” for example, included calls for “unceasing pressure for penetration.”The American military establishment created in the 1940s turbocharged earlier approaches to national security, moving limited spending and retrenchment between conflicts to proactive and perpetual preparedness. Because the world continued to be seen as a dangerous place even after 1945’s victories, expanding military power was prescribed to deter aggressors or to prevail over them if push came to war.Emphasis on “the world” helps to explain the scale of power. Air power and other technological advances (in communications, for example) created the integrated international arena in which American leaders acted after the defeat of the Axis powers in the Second World War.There was a rapid and dramatic growth in the policy agenda. For the new Department of Defense, this meant unparalleled budgets: US$997 billion by 2024 compared to China’s US$314 billion (greater than any other countries in the 1940s and ever since). It also produced global reach greater than any empire in history: there are almost three million members of the U.S. armed forces today, based in 70 countries. American powerTrump fails to grasp (or chooses to ignore) the fact that this vast power was used regularly and aggressively:There were large-scale interventions from Korea and Indochina to Kuwait, Afghanistan and Iraq.There were massive transfusions of equipment, training and personnel into NATO and other countries on every continent, including Israel, Pakistan, Brazil and Australia. There was Pentagon co-operation with other agencies engaged in all-of-government efforts — overt and covert operations that ranged from intelligence gathering (including espionage), destabilization and coups (for example in Iran, Guatemala, Chile) and assassinations (including repeated attempts on Cuban leader Fidel Castro and the frequently assumed association with the deaths of Congolese independence leader Patrice Lumumba, Dominican dictator Rafael Trujillo and South Vietnam’s Ngô Đình Diệm.“Defence” served both as the foundation and the justification for the evolution of many elements of this repertoire over the decades.FailuresA cost accounting of aggressive/offensive defence in the past is disturbing. The tabulation of a 75-year record has filled countless volumes, but two striking examples attest to some major failures:A lack of “winning” in large-scale military operations: A “truce” in the Korean peninsula in 1953, giving way to failures in Indochina, Iraq and Afghanistan. (Success in Kuwait in 1990-91 does not significantly alter this problematic balance.)Continued independence and resistance from states once thought weak enough to be managed, in particular Cuba and Iran.Dubious results also had staggering price tags. There were 36,000 American deaths in Korea; 58,000 in Vietnam; 7,000 deaths and 53,000 wounded military personnel in Iraq and Afghanistan. Trillions of dollars were devoted to defence spending at the expense of economic and social programs on the home front. Trump seems to believe that, with the Department of War, he’s replacing post-1945 defence policies rather than doubling down on them, meaning he is intensifying the offensive/aggressive approaches without grappling with their flaws. In particular, he has no apparent grasp of what bedevilled the post-1945 American drive for global domination.American arroganceDemocratic Sen. J. William Fulbright famously critiqued the “arrogance of power” in the 1960s, countering the U.S. presumption of a right to impose values on distant corners of the world like Southeast Asia. Other critics of the Vietnam War further questioned whether the U.S. had sufficient manpower and intellectual or economic resources to achieve its goals. Wasn’t the world too large and complex, with too many rival players and independent allies, and too many ever-evolving challenges, for one country to imagine holding global management capacities in its hands?In recent years, former presidents Barack Obama and Joe Biden began to apply a pragmatic calculus to conflicts in Iraq and Afghanistan, even if their core vision continued to exhibit historic “Manifest Destiny” concepts. One example is Obama’s attempt to determine an effective troop level in Iraq while simultaneously retaining his faith in American “exceptionalism.”Trump’s determination to go on the offensive threatens to reverse even tentative adjustments to American aspirations of global domination. He is reviving attitudes like those of former secretary of state Condoleezza Rice early in the Afghanistan war, when she chided cautious generals by saying “I’m an American. Nothing is impossible.” Read more: Out of Afghanistan: Joe Biden and the future of America's foreign policy Trump’s threatsThe magnitude of Trump’s ego (his “I alone” mentality) risks intensifying such a revival — with potentially serious consequences.Attacks on Venezuelan boats said to be carrying drugs, a failure to rein in Israel’s expanding campaigns in Gaza and the deployment of National Guard forces to Los Angeles, Washington, D.C. and Memphis are strong hints of what may be coming. Recalling Trump’s speculations about military operations against Greenland and Canada just months ago makes it impossible to dismiss anxiety about his intentions.Ronald W. Pruessen has received past research grants from Social Sciences and Humanities Research Council of Canada.