The main objective at the conference was to decide on what to do with Nazi Germany once Adolph Hitler was finally defeated. Stalin's army was stationed just 65 kilometres from the gates of Berlin, and the Allies were fighting on Germany's western border.
France had been liberated along with Belgium. The Nazis had also been driven out of Poland, Romania, and Bulgaria. It wasn't a question of whether Hitler would fall, just how and when.
The Big Three demanded the unconditional surrender of Germany. They promised not only to de-militarize and de-Nazify the country, but also to hold it accountable for the wanton destruction it inflicted on all four corners of the globe.
They were determined to have it pay for the reconstruction of Europe, along the lines of the settlement of World War I.
Hitler and his top officers were to be put on trial and subsequently executed. Germany would then by divided into four zones controlled by the US, British, Soviet and French armies.
Charles de Gaulle had noticeably been left out of the Yalta Conference — he was not invited— and Stalin only agreed to give him a sphere of influence in Germany if it were taken from the spheres of Great Britain and the US.
In parallel to all of that, Roosevelt and Churchill wanted to create a new world order, with self-determination for the liberated people of Europe and collective security through the United Nations.
Stalin, however, had other plans.
Everybody in Yalta, including Stalin, knew that the US was badly in need of his backing for its war with Japan. He agreed to join that battle on three conditions.
The first was that he would not commit until after the defeat of Germany. Secondly, he insisted Roosevelt and Churchill allow him to re-take Japanese territory that Russia had lost during the Russo-Japanese War of 1904.
Third was formal recognition of Mongolia's independence from China (it had been a Soviet satellite since 1924).
Roosevelt agreed to all of Stalin's conditions, then moved to the second item on his agenda: the United Nations, which was due to replace the now largely dysfunctional League of Nations.
The Americans never joined the League, even though it had been initiated by their own president, Woodrow Wilson, towards the end of World War I.
Roosevelt wanted to give the world the UN, and have his country seated first at its founding conference.
The idea of the UN was Roosevelt's brainchild from as early as 1941. Stalin's acceptance of the UN was conditional on the Soviet Union having a permanent seat on the Security Council along with veto power over any unwanted resolutions.
That was agreed straight away at Yalta, rights that were subsequently bequeathed to modern Russia after collapse of the Soviet Union in 1991.
Stalin had also demanded automatic UN membership for 16 Soviet satellites, but only two were admitted, one being Ukraine.
Once through with milking Roosevelt for concessions, Stalin turned to Winston Churchill.
The British leader was seeking a deal sought by the London-based Polish government-in-exile, and asked Stalin for free and democratic elections not only in Warsaw but throughout Eastern European states being liberated from Nazism, including Czechoslovakia, Hungary, Romania, and Bulgaria. Stalin committed with very vague language, but made strict demands regarding Poland, which he said, had twice been used by the Germans to invade his country.
He vowed for that never to happen again, refusing to return parts of east Poland that the USSR had annexed in 1939, adding that he would not recognize the Polish government-in-exile.
Their demands, he noted, were simply un-negotiable. World War II had been triggered by the 1939 invasion of Poland and it concluded with Poland being ceded to the USSR.
When world leaders met in the UN founding conference in San Francisco that April, Poland was not invited. It was given no free election and became a Soviet satellite, as did other East European countries.
Apart from lip-service protests, neither the US nor Britain did anything to stop that.
Blame for this lies not with Roosevelt and Churchill themselves, but their successors.
By the summer of 1945, these two men, so recently remaking the world round the table at Yalta, were out of power. Stalin stayed in charge for another eight years, until his death in 1953.
Roosevelt died in April 1945 while Churchill was replaced by Clement Attlee in July that year — a man with all of Churchill's weaknesses and none of his strengths.
When the US president brought the terms of the agreement home, hopes were still high. Roosevelt addressed Congress with much optimism about what had been achieved at Yalta, saying: "I come from the Crimea with a firm belief that we have made a start on the road to a world of peace."