Internationalism

Internationalism was the conviction that the United States could not secure peace by retreating behind its geographical boundaries: it had to work with other nations and help build institutions capable of preventing another war. In Harry S. Truman’s account of the postwar order, cooperation was an ambition, not a guarantee. His commitment to it persisted through disputes with the Soviet Union and the decision to use atomic weapons against Japan.

From wartime purpose to postwar order

At the 1944 Democratic convention, Franklin D. Roosevelt set out a two-part task: to win the war quickly and to form worldwide international organizations able to use the armed forces of sovereign nations to prevent another war. Truman’s campaign echoed that purpose. He argued against a postwar return to Republican isolationism and presented continued international engagement as part of securing both victory and peace.

The position was not merely a campaign contrast. In a major address, Truman argued that isolationism had passed and that geographical barriers could no longer provide safety. He called for a strong, lasting United Nations and framed the responsibility of a great power as service rather than domination. The address also registered a political connection between president and audience: a contemporary observer described a bond of friendship between Truman and the people listening.

Cooperation under pressure

International cooperation, in Truman’s view, depended on trust among the major powers and confidence among smaller nations. In private, he wrote that the three great powers would need to trust one another and honestly want peace; he also recognized that smaller countries lacked confidence in both the Soviet Union and Britain. His willingness to pursue peace therefore did not rest on assuming that disagreement would disappear. He acknowledged that complete Soviet cooperation was unattainable, while hoping for substantial cooperation, and was prepared to press the Polish question against the commitments made at Yalta.

The resulting approach combined negotiation with firmness. Truman believed workable relations with the Soviet Union remained possible if both sides made concessions, but he also warned that failure to settle the Polish issue as agreed could lead the Senate to reject American participation in the United Nations. His internationalism thus involved a domestic constraint as well as a diplomatic one: American participation in a common postwar order depended, in part, on whether the administration could defend its agreements and choices at home.

Peace, force, and the atomic decision

Truman’s internationalism was not a pledge to avoid force at any cost. As the war with Japan continued, the administration’s advisers considered whether an atomic weapon could be demonstrated harmlessly or used against a military target before cities were attacked. A technical demonstration was rejected as unlikely to produce the decisive shock sought to induce surrender; with only one bomb expected to be ready at first and uncertainty about whether it would work, a failed demonstration could strengthen Japanese resistance. The recommendation instead favored direct military use.

At Potsdam, Truman recalled a consensus among senior advisers that the bomb should be used, including the view that an invasion of the Tokyo plain could cost at least a quarter of a million American casualties. He later described his own decision as the result of long and careful thought and made clear that he disliked the weapon. Those arguments placed the pursuit of a swift surrender and the saving of lives alongside the prospect of catastrophic harm to civilians; they did not erase the moral cost of the choice.

That cost remained visible in Truman’s response to a demand for still more destructive action. On August 9, he wrote that he would not destroy whole populations unless it was absolutely necessary, expressed hope that Japan would surrender after the Soviet Union entered the war, and emphasized his concern for Japanese women and children as well as American lives. That evening, he urged Japanese civilians to leave industrial cities. His statements show international responsibility extending beyond the United States, even while his government pursued the surrender of an enemy through overwhelming force.

The limits and stakes of the principle

The evidence presents internationalism as an effort to replace isolation with organized cooperation, not as confidence that every government shared American purposes. Truman’s insistence on a durable United Nations stood beside his doubts about Soviet conduct in Eastern Europe; his pursuit of peace coexisted with readiness to fight for it. The tension was central to the principle as he applied it: international institutions required participation and trust, but their credibility also depended on confronting broken agreements and continued war.

The atomic decision exposed a further limit. Truman sought to end the killing and avoid the expected costs of invasion, yet the means considered and chosen threatened mass civilian destruction. His expressed reluctance and concern for Japanese civilians did not resolve that contradiction. Instead, the contrast clarifies the demands of his internationalism: a postwar order had to restrain future conflict, while decisions made to bring the existing war to an end carried consequences that the language of peace could not make harmless.