International relations theory gives weight to impersonal factors such as the cold calculations of national interest by different states and their cooperation, competition and conflict. But the return of Donald Trump as president, whose actions on trade, technology and security threaten to shake up global affairs, is a reminder that history is also shaped by the agendas and personalities of leaders, including their personal strengths and weaknesses, their idiosyncrasies and their hobbyhorses. Decisions and actions of national leaders guide international relations. As the UNESCO constitution states, “since wars begin in the minds of men, it is in the minds of men that the defenses of peace must be constructed.” In high-level diplomacy, personal bonds between leaders can make a significant difference. And Trump is a great believer in the notion that relationships between leaders can positively mold ties between nations. In his first term, Trump pursued a personalized approach to diplomacy to help shape U.S. relationships with key countries. In 2019, he became the first sitting American president to set foot in North Korea, crossing the Demilitarized Zone for a brief meeting with dictator Kim Jong Un. And the volatile Middle East moved toward stability as Trump, far from starting a new war, brokered the Abraham Accords. But Trump’s use of diplomacy to steer relationships from confrontation to cooperation and to end wars (like in Afghanistan) came under withering criticism from commentators and opponents, who wanted him to wield American power assertively. Many world leaders pursue personalized diplomacy. They give diplomatic moves their imprimatur through social media posts under their names. Understanding the role of personal factors is important in the study of interstate relations. The power of interpersonal relations in statecraft also extends to the knowledge gained about counterparts’ personalities through private interactions, which can strengthen one’s hand in negotiations. Trump is first and foremost a dealmaker who views diplomacy through the prism of potential transactions. This makes personalized diplomacy — and personal outreach to other countries’ leaders — critical to his efforts to advance American interests. In fact, he often employs the tactics he outlined in his 1987 book, “Trump: The Art of the Deal.” “A little hyperbole never hurts,” Trump wrote of his deal-making, which he said could also be advanced through some flattery, cajoling and hardball tactics, including seeking to pummel the other side. In his search for deals, Trump has not hesitated to flatter foreign leaders, including dictators, even as his threats remain barely disguised. For example, Trump has called Chinese President Xi Jinping “a brilliant man” and “a very good friend,” and said “nobody in Hollywood could play the role of President Xi.” And he has said that Russian President Vladimir Putin, like Xi, is “smart” and “tough.” Trump has praised Turkish President Recep Tayyip Erdogan for getting “very high marks” for governing “very, very strongly.” And after meeting Kim, Trump said, tongue-in-cheek, “We fell in love.” Trump has reportedly expressed interest in making an early visit to Beijing. While the Chinese Communist Party finds Trump’s unpredictability somewhat perturbing, it must love his transactional approach to foreign policy, as the ruling party also likes to cut deals. In fact, assertive mercantilism is a central leitmotif of China’s foreign policy. More fundamentally, Trump has upended traditional ideas about leadership and diplomacy through his complex personality, which blends refreshing candor with deliberate combativeness, braggadocio and grandiosity. And unlike former President Joe Biden, Trump isn’t scripted, as his freewheeling speeches and news conferences underscore. Trump is known to talk tough. But his tough talk does not often translate into action. His Iran policy in the first term included withdrawing from the 2015 nuclear deal with Tehran, reimposing sanctions and assassinating in Baghdad by drone strike Iranian Gen. Qassem Soleimani. Yet Trump was reluctant to take on Iran directly lest it embroil the U.S. in another war. In 2017, Trump threatened “fire and fury” unless North Korea halted its nuclear-weapons program. But just months later, Trump embraced Kim in Singapore in the first-ever U.S.-North Korean summit. When Trump’s threats center on more realistic action, such as slapping trade tariffs or stepping up or putting on hold military support to an ally, he is able to win through intimidation. Recently, Trump helped secure a Gaza ceasefire deal by warning that there would be “all hell to pay” if the hostages were not freed by his inauguration day — a threat aimed at not only Hamas but also Israel. And through his pre-inauguration threat to impose a 25 percent tariff on all Canadian exports to the U.S., Trump precipitated a crisis in Canada’s governing Liberal Party that proved the last straw for the deeply unpopular Prime Minister Justin Trudeau, who decided to resign. Indeed, Canada has announced a slew of border-security measures to address Trump’s main concerns — illegal border crossings by migrants and the smuggling of illegal firearms and drugs into the U.S. Trump basically is a pragmatist. Despite his thunderous criticism of China as an economic predator, Trump did not impose any sweeping trade sanctions against China in his first term, choosing instead to employ the tariff card, while sprinkling some flattery on Xi. Railing against “endless wars,” Trump finished his first term as the first American president since Jimmy Carter not to start a new war. And he wishes to have a similar record in his second term, saying he wants to be a “peacemaker” who builds the world’s strongest-ever military whose success would be measured “not only by the battles we win but also by the wars that we end — and perhaps, most importantly, the wars we never get into.” But that has not restrained Trump’s expansionist itch, including taking back the Panama Canal and buying Greenland from Denmark. He has invoked the notion of “manifest destiny,” which drove 19th‑century U.S. territorial expansion. Real political power comes not from the office a politician holds but from the way a leader is able to change people’s thinking. That power lasts beyond the leader’s term in office. The international power of Trump’s conservative populism will extend beyond his lifetime. Brahma Chellaney is a geostrategist and the author of nine books, including the award-winning “Water: Asia’s New Battleground.”