to argue that the British opposed Russia whereas the USA and more specifically FDR appeased them is garbage.
Churchill had already agreed to Soviet control of Romania, Bulgaria, Hungary and to some degree Poland in Moscow in October 1944. Britain had voted with the Russian at the European Advisory Committee to divide Germany into different equal zones of control, giving the east to the USSR, and also in moving the Soviet and Polish borders westwards therefore moving soviet influence west.
Accounts from Yalta which are critical of FDR's involvement tend to be from British arch-americanophobes (if thats a word) and lurid allegations from McCathyite republicans in the 1950's.
Yalta was in Feb 1945, the detonation of the first atomic bomb was on July 16, 1945, prior to this the allies didnt have the military strength to force the USSR to surrender its aquisitions in Eastern Europe even if they wanted to. They still believed they needeed the USSR to assist in the invasion of Japan, due to the very high losses this would involve.
No accounts of Yalta at the time described FDR as having diminishing mental powers. Harriman describes his as 'worn, wasted but alert'. James Brynes 'marvelled' at his mastery and presentation of material at the conference. Stettinius described his performance as 'a definitive answer to the sensational storied without foundation that circulate about his health'. The theory that FDR was unfit physically and intellectually stem from primarily an allged statement from Hopkins to Halifax after FDRs death that FDR did not follow half of what occured there. Neither Halifax nor Hopkins accounts can be trusted. Hopkins son Robert was present as a military photographer and declared that FDR was alert at all times and that his father had made no such statement. Halifax only began to put forward this claim about Hopkins after FDR and Hopkins death.
The British had from start of the USA invovlement in WW2 been pushing for invasion of parts of Europe, such as Italy and Norway, which would have resulted in the Russians seizing more of Europe than they did anyway. Churchill opposed the Normandy landings and after they took placed pushed for allied involvement in minor theatres.
FDR did not gamble the national interests of the USA, the cause of democracy, or the sacrificies of the US armed forces at Yalta. He believed that the USSR could be contained and would one day be overwelmed by democratic forces. and it was. At the time no one could prevent Stalin consolidating his hold on Eastern Europe without the cost of another war which would be unthinkable. FDR limited the power of the USSR by refusing to share atomic secrets, basing US troops in Germany, aquired naval bases in the pacific and atlantic, prevented Italy, Greece and Yugolsavia from falling into the Soviet sphere, and encouraging China as a great power to counter balance the USSR.
What the Soviets 'won' at Yalta their armies already possesed, if it was such a success why did the USSR violate so many of its clauses?
I havent finished this post but I want to go to the pub. I will add some more tomorrow.