September 1, 1939

September 1, 1939, marks the outbreak of war in Europe and a hinge between the political debates of the 1930s and the mobilization that would bring J. Robert Oppenheimer into wartime atomic research. The date matters not simply as a calendar marker: it locates his arguments about the Nazi-Soviet pact, the future of American liberal politics, and the danger of war within the crisis as it unfolded, before later nuclear-policy disputes gave those arguments new significance.

The outbreak in Europe

One week after the Soviet Union announced its nonaggression pact with Nazi Germany, war began with the invasion of Poland. The pact had stunned observers and unsettled left-wing intellectual circles, where many American Communists left the Party. Haakon Chevalier remained loyal to the Communist Party USA and defended the agreement as a strategic necessity. In September 1939, he and hundreds of others signed an open letter rejecting the claim that the Soviet Union and totalitarian states were fundamentally alike.

The political shock of the pact formed the immediate background to Oppenheimer’s response to the outbreak of war. In a letter to a fellow physicist, he treated the pact with skeptical humor, while withholding judgment about what would follow. The episode captures a moment of uncertainty rather than a settled political position: the European crisis had made familiar ideological explanations harder to maintain, but its consequences were not yet clear.

Oppenheimer and the pact

Oppenheimer’s name did not appear on the open letter defending the Soviet position. Chevalier later recalled that, in the fall of 1939, Oppenheimer analyzed the pact for others, arguing that it was less an alliance than a treaty of necessity shaped by Western appeasement of Hitler at Munich. Chevalier remembered him as a lucid and persuasive explainer, able to address the misgivings of people who found the Soviet-German agreement disturbing. This account presents Oppenheimer not as a signatory to the defense of the pact, but as someone trying to interpret it within a rapidly changing political landscape.

That distinction matters because Oppenheimer’s political activity did not fit neatly into a single label. His later association with left-wing causes and friends made his conduct a subject of scrutiny, but the evidence around September 1939 shows debate and interpretation, not a simple declaration of allegiance. The war’s outbreak sharpened questions about the relationship between anti-fascism, Soviet policy, and domestic politics; it did not resolve them for him.

Political writing in the war’s shadow

The arguments continued in pamphlets circulated in 1940. Oppenheimer was not a member of the League of American Writers, but he edited a pamphlet as a favor to a friend; it argued passionately against American entry into the European war. He may also have helped prepare two reports titled Reports to Our Colleagues, issued in February and April by a California college-faculties committee associated with the Communist Party. More than a thousand copies were mailed to people at universities on the West Coast. Chevalier said Oppenheimer drafted the reports and paid for their printing and distribution; another associate corroborated his involvement in their production, while the evidence did not establish that Oppenheimer was their sole author.

The February report argued that the European war was changing American politics: it saw the New Deal under attack, liberal support for a democratic front weakening, and red-baiting becoming widespread. The pamphlets also defended domestic social programs and criticized the movement toward armaments. A later report described Franklin D. Roosevelt as having become a reactionary and a warmonger. The biographical account treats Oppenheimer’s authorship of that language cautiously: his correspondence indicates disappointment with Roosevelt, but not clear support for so sweeping a denunciation. If he helped draft the pamphlets, the record suggests that his central concern was the effect of the war on American domestic politics.

From political crisis to scientific mobilization

The outbreak of war coincided with a growing recognition among physicists that an atomic bomb might be possible. Oppenheimer and others had understood the possibility as early as February 1939. Before war began in Europe, Leo Szilard had persuaded Albert Einstein to warn Franklin D. Roosevelt that a new kind of bomb could be extraordinarily destructive and that Germany might be pursuing one. The warning led Roosevelt to establish a Uranium Committee, though little progress followed for nearly two years. British assessments later strengthened the case for urgency, and the United States created the Office of Scientific Research and Development in 1941 to mobilize science for military purposes. September 1 therefore belongs to the political beginning of the European war, not to the start of the atomic project itself; it marks the wider crisis in which that project would acquire urgency.

The date also opens onto Oppenheimer’s later public role, without making his subsequent positions inevitable. In 1949, amid debate over the hydrogen bomb, he found George Kennan’s proposal for a moratorium on its development reasonable, while warning that officials in Washington would regard such proposals as dangerous. The contrast between Oppenheimer’s 1939 effort to interpret a European political crisis and his later arguments about nuclear policy shows how his public concerns changed with the stakes of the moment. The outbreak of war is a starting point in that history, not an explanation that erases its uncertainties.