The Tehran Conference, code-named Eureka, was a meeting, in November-December 1943, of 'the Big Three' Allied leaders: Roosevelt, Stalin, and Churchill. The conference in Iran aimed to decide how the Second World War (1939 to 45) against Germany and Japan should proceed militarily, when an invasion of Western Europe would be conducted, and who would control what in Central and Eastern Europe after victory was achieved.

President of the United States Franklin D. Roosevelt (1882 to 1945), leader of the USSR Joseph Stalin (1878 to 1953), and British Prime Minister Winston Churchill (1874 to 1965), collectively called 'the Big Three,' met in person at the Tehran Conference in Iran from 28 November to 1 December 1943. The three main Allied leaders hoped to thrash out a mutual strategy that would win them the war against the Axis powers of Germany, Japan, and Italy. Each leader was accompanied by a team of military chiefs of staff, advisors, and diplomats, including the British foreign secretary, Anthony Eden, and the Soviet foreign minister, Vyacheslav Molotov.

This was the first time the three leaders had all met together. Roosevelt and Churchill had met at the Casablanca Conference in January 1943 and had just met again in Cairo a few days before the Tehran Conference to thrash out a united front to present to Stalin; Churchill had met Stalin in Moscow in 1942. The US president felt that he could 'charm' Stalin to come around to his way of thinking, and to this end, Roosevelt accepted Stalin's offer and stayed at the Soviet embassy, which was also the host venue of the conference. Roosevelt's aim to significantly influence Stalin's thinking was an ambition never quite realised.

Relations were cordial between the leaders, a situation helped by the dinner to celebrate Churchill's 69th birthday on 30 November, at which he was given a Persian lamb's wool hat. Another gift, given the day before, was the Sword of Stalingrad, a ceremonial sword commissioned by King George VI of Great Britain (reign 1936 to 1952) and presented to Stalin to celebrate the Soviet victory over a German army at Stalingrad the year before. The sword had the following inscription: "To the steel-hearted citizens of Stalingrad, the gift of King George VI, in token of the homage of the British people" (IWM).

So far in the war, Germany had occupied most of Europe and had launched an attack on the USSR with Operation Barbarossa in 1941. The Eastern Front settled down to a war of attrition, but Germany had then suffered a catastrophic defeat at the Battle of Stalingrad in February 1943 and another one in the Battle of Kursk in August. Italian forces had been defeated in North Africa, but reinforcement by Germany's Afrika Korps had reignited that front until the British had won a decisive victory at the Second Battle of El Alamein in November 1942. Southern Italy was then invaded, and its government collapsed in September 1943.

Japan's attack on the US base at Pearl Harbour had brought the United States into the war in December 1941, and so the Pacific War was ongoing. Allied forces had meanwhile made impressive gains in South East Asia and begun an invasion of Burma (Myanmar). It was felt that the military successes combined with the massive economic and military resources of the US would ensure, sooner or later, an Allied victory in the war. In short, the Allied leaders were in a confident mood at Tehran, confident enough to begin discussing what the post-war world would look like.

The most immediate question to address was how, when, and where the Western Front would be reopened, creating a 'second front' against Nazi Germany. Hitler had stopped short of invading Britain because he could not establish air superiority in the Battle of Britain. The United States, Britain, and their allies were now steadily amassing men and material ready to launch an invasion of Western Europe, an operation code-named Overlord.

Stalin wanted the Western Front to begin as soon as possible and so relieve the tremendous pressure on the USSR. The Allies were more cautious. An amphibious assault on Continental Europe would be difficult and inevitably costly in lives. The invasion must come with overwhelming force if it were to succeed. The Allies wanted the USSR to launch an offensive in the east to coincide with the invasion to fully occupy German forces. To this, Stalin agreed. The main invasion was planned for Normandy in May 1944 (in the event D-Day was delayed by a month), while a secondary invasion would simultaneously be conducted from the Mediterranean and strike through southern France.

Churchill also wanted a third point of attack, to continue the push into (German-controlled) northern Italy and the wider Mediterranean, but both Stalin and Roosevelt felt this would weaken the attacks on France, which must remain the main focus of the operation. In order to confuse the German high command and have them send resources where they would not actually be needed, all three allies agreed to cooperate in devising various plans of subterfuge. Who exactly the commander-in-chief of Overlord would be was left to a future conference.

Other issues discussed at Tehran included how to bring Turkey into the war on the Allied side. It was agreed to support the communist partisans and their leader, Josip Broz Tito (1892 to 1980), in Yugoslavia. Stalin promised that the USSR would join the fight against Japan once Germany had been defeated in Europe. Another issue settled in Tehran was the declaration that Iran, then occupied by Allied forces, would be declared an independent state.

What exactly to do with Germany should victory be achieved was not yet agreed upon. The key consideration was to ensure the nation did not pursue new aggressions in the future, but also that it was not dealt with so harshly that a lasting resentment was created. This is precisely what had happened after the Treaty of Versailles, which had concluded the First World War (1914 to 18). The objective this time was that peace should not be a fleeting pause in a century already blighted by two major conflicts. To this end, Roosevelt more or less convinced Stalin and Churchill to endorse some kind of peace-keeping international organisation, a successor to the League of Nations, created in the spirit of the January 1942 'United Nations Declaration,' which had been signed by the USSR, Britain, the USA, and China.

Ideas floated around to ensure a peace-loving Germany included breaking it up into its individual states (which Stalin favoured), splitting it in half along a north-south line (suggested by Churchill), or keeping it as a whole but having the Allies effectively run the country or parts of its vital industry and economy in some sort of joint governance (Roosevelt's position). It was agreed that Austria, joined with Germany in the Anschluss of 1938, should have its independence restored. Germany should also be made to pay some sort of financial compensation to the victors and the territories it had (and still) ruthlessly occupied.

The future of both Poland and Finland was also discussed. Stalin wanted to keep the occupied territory allocated to the USSR in the 1939 Nazi-Soviet Pact and have access to the Baltic coast via East Prussia, effectively, then, control of all of Eastern Europe and most of Central Europe. Roosevelt and Churchill hoped that developments during the war might reduce this claim, but it was recognised that if the USSR's Red Army occupied Europe up to and including Germany, there was not much that could be done about it afterwards.

Stalin was a wily negotiator, and his invitation to have Roosevelt stay at the Soviet embassy paid dividends. Firstly, the Soviets were able to keep a close eye on the US delegation. Secondly, it prevented Roosevelt and Churchill from more closely colluding. Churchill was certainly not happy with the accommodation arrangements:

The British Prime Minister recalled, in his own memoirs, how he felt obliged to seek a private interview with Stalin to complain that Roosevelt now seemed to be avoiding him, and to counteract what he saw as the Soviet leader's attempts to split the Anglo-US alliance by exploiting Roosevelt's goodwill and what many regarded as a naïve idealism in his approach to world affairs.

(Imperial War Museums)

Roosevelt and Churchill at least agreed that, should the worst happen and the Red Army occupied most of Poland before the western Allies got there, Poland could be compensated by extending its western border at the expense of a defeated Germany. Stalin was adamant that the current Polish government, then operating in exile in London, would not be involved in Poland's future, largely because some of its members, he felt, were guilty of negative propaganda against the USSR. These issues, collectively called the 'Polish Question,' and many others would have to be discussed at future conferences.

The Allied leaders would meet twice again, with some changes in leadership, in 1945. The Yalta Conference in February 1945 again involved Roosevelt, Churchill, and Stalin. It was decided that Germany and Austria would be divided into four zones of occupation with a joint military government established in each. The respective capitals of Berlin and Vienna were similarly divided into zones of control. A new set of borders for Poland was agreed upon; the western border, as proposed at Tehran, would be shifted westwards at the expense of Germany. A promise to hold free elections in Poland was never met by Stalin. Regarding Japan, Roosevelt and Stalin made a deal that, in return for Russia entering the war against Japan, certain Soviet land demands in Asia would be met. Other matters discussed included Germany's reparations, the formation of the United Nations, and organising public trials for war criminals.

It was felt by many that Roosevelt and Churchill had negotiated away control of Eastern Europe to the USSR at Yalta, but the reality was that the Red Army already had control of this part of Europe. A follow-up meeting, the Potsdam Conference, was held from July to August 1945. With victory in Europe now achieved, the new US president, Harry S. Truman, Churchill, and then his successor, Clement Attlee, and Stalin met at Potsdam. A surrender ultimatum was issued to Japan, known as the Potsdam Declaration. The ultimatum was ignored until US aircraft dropped atomic bombs on the cities of Hiroshima and Nagasaki. Japan surrendered on 14 August. All parties at Potsdam had agreed to allow democratic elections in countries Nazi Germany had occupied, but this was not carried out in the USSR's half of Europe. The resulting mutual suspicion between East and West meant there would be no more conferences of Allied leaders as the world entered a new era, the Cold War.