The Big Three proved that alliances can be forged regardless of recent histories of animosity and discord. The United States and the Soviet Union did not have any diplomatic contact until 1933, the year that Hitler became Chancellor of Germany, and the British and the Soviets ceased diplomatic contact between 1927 and 1929. Before the United States decided to join the war, there was a great deal of distrust between the United States and Britain, and the unity they achieved during the war is one of their great accomplishments. Churchill and Roosevelt were very different, and Roosevelt generally didn't like the other's political views. He was for social reform, and Churchill was labeled a conservative. Roosevelt outranked Churchill, and his country had more potential political power, thus, Churchill never dared to oppose him entirely. They also had different ideas regarding empire. In defining the freedom of self-government, Churchill meant only freedom for those that had been overtaken by the Nazis. He wanted to rid Europe of Hitler, and then return to the pre-war status quo, while Roosevelt hoped to extend these ideals further.

However, these obstacles were slight in comparision to what had to be overcome in dealing with the Soviet Union. The Bolshevik Revolution had made the United States and Britain hostile to the Soviet Union, and the presence of capitalism in the West made the feeling mutual. Churchill was even an advocate in 1919 of Allied military intervention in the Soviet Union. He was quite open in saying that he had fought against Communism, but he now saw that the British and Soviets had a much greater common threat, and so their paths were, at the moment, the same. But once this danger was eliminated, he would again see Communism as his adversary. Both the West and the USSR had secretly hoped to steer the Germans towards the other, and let them wipe each other out.

Nonetheless, triangular communication between the Big Three began in the summer of 1941. It was at this point that all three countries recognized the need to bind together for survival against a common enemy, and so formed the Common Law Alliance. Prior to this the Soviet Union had held onto the option of making peace with Hitler, as well as becoming allied with Britain and America. However, when Hitler ignored Stalin's virtual acceptance of the invitation into the Tripartite Pact (Germany, Italy, and Japan), and instead invaded Russia in June 1941, Churchill jumped to bring aid and create a true alliance. The Soviets did not leap into the Anglo-American boat immediately, as joining forces with the Western Allies went against Socialist principles. Stalin had to ease his people into such an odd partnership, as the Marxist point of view actually predicted that Hitler, the United States, and Great Britain would join together against the Soviet Union, because they all had the same fundamental basis of capitalism.

However, Churchill sent another, more personal note, to Stalin, and this led to Stalin's acceptance of British friendship and eventually Lend-Lease aid from the United States. Stalin proceeded to ask for British "active military aid," the denial of which was a source of argument until Teheran two years later. The United States' polices towards Russia generally followed the decree of public opinion, and the turning point between the two nations was the Russo-German war. As the Soviets persevered much much longer than expected in the battle against the Germans, the American people softened. They became much more convinced that whoever was fighting Hitler was their ally, regardless of the fact that a Communist dictatorship was really as much of an enemy to them as was a Nazi one.

But there remained a definite distinction between this relationship and the one between Churchill and Roosevelt. The Western Allies consistently feared losing Stalin to Hitler, and so were afraid to anger him, and their communication with him was much less frequent. Stalin, who was often called "Uncle Joe" by the other two, tended to alter the truth to extract what he wanted. At times when he needed more help, he would say that the Soviet army would soon be no longer able to "render assistance to its allies," while later, when his nation's situation was no different, he would say that Germany was sure to quickly break down. But Churchill and Roosevelt were able to see through him much of the time, whereas some sources believe that Stalin truly did not understand the West. It was not clear to him why they could not make decisions immediately, without consulting others, as he could. His mannerisms could switch instantaneously from being insulting to courteous, and he was constantly testing his allies for their loyalty. The tone of discussions between Stalin and the other two was often decided by how well the Russian army was doing at that moment. In general, he was cordial to Roosevelt, for he respected the United States, but for some reason he was particularly rude to Churchill. There were often tensions between these two that Roosevelt had to smooth over with humor. In some ways, Roosevelt advocated an appeasement policy towards Stalin, as he commented, "I think that if I give [Stalin] everything I possible can, and ask for nothing from him in return, noblesse oblige, he won't try to annex anything and will work with me for a world of peace and democracy." Churchill on the other hand, deliberately steering clear of the mistakes of his predecessor, Chamberlain, did not want to back down to Stalin's demands. But Roosevelt understood that the Red Army held the upper hand, as they had control of the ground in Europe, and that concessions had to be made to get their main goals accomplished.

Anglo-American cooperation began prior to all this with the exchange of intelligence and supplies, after being somewhat shaky between the two world wars. Harry Hopkins, one of Roosevelt's main representatives, spent six weeks with Churchill in 1941, and this greatly encouraged the personal, not just political, relationship between Churchill and Roosevelt. The first summit meeting between these two was August 1941, at the Atlantic Conference, during which they were able to evaluate one another. At this point, Churchill was desperately trying to draw the United States into the war, but there is no evidence suggesting that he affected the eventual military actions of Roosevelt. They did send a joint message to Stalin pointing out the necessity of their cooperation. In December 1941, Churchill and Roosevelt created the Grand Strategy for the war at the Arcadia Conference. Stalin continued to refuse to journey outside of his country so as not to lose contact with his front lines, but he still became upset when left out of anything, as he was especially concerned with being involved in post-war decisions. He feared that Germany would not be sufficiently punished so as to not pose a threat to him. Roosevelt was also very anxious to meet with Stalin, but this did not happen for some time.

So while Stalin remained in Moscow, Churchill and Roosevelt's relationship continued to grow. Their meetings were brimming with ceremonial gestures of cameraderie. Churchill declared, "The Prime Minister of Great Britain has nothing to hide from the President of the United States," and he stayed at the White House during diplomatic ventures to meet with his counterpart. Roosevelt told Churchill that "It is fun to be in the same decade as you." It seems that to some extent the two were trying to bring a sense of unity and hope to their nations' war efforts through their friendship.

Stalin began to press his demands that he be allowed to regain territory in the Baltic States and Poland, but the United States remained firmly against this, and the British followed their lead. Thus, Stalin gave a speech, which the West interpreted to mean that Stalin was looking to negotiate a separate peace with Hitler or the German people, and this pressure was enough to get his allies to give in regarding the Baltic States. Poland remained an issue to be dealt with. The Casablanca, Trident, Algiers, and Cairo Conferences followed, and although Roosevelt desperately sought to meet Stalin in person, this still did not transpire.