The Western Allies had very limited ability to help eastern European countries that the Soviets had invaded. Contrary to the belief of some that they could have continued advancing to Moscow in spring 1945, they lacked the strength to do that by conventional warfare, and their populations were growing tired of war.
There's a revealing passage in War Diaries 1939-45, by Alan Brooke. He was Chief of the Imperial General Staff, the professional head of the British Army, from December 1941 and Chairman of the Chiefs of Staff Committee from March 1942. He was a member of the US-British Combined Chiefs of Staff committee from its creation in April 1942. With all these roles, he dealt with strategy world-wide. His private diary was rather open about everything he did and thought, and you need a modern edition: the volumes published in the 1950s edited by Arthur Bryant have been ... excessively bowdlerised and tittivated.
In the entry for 24th May 1945, he writes:
This evening I went carefully through the Planners' [Joint Planning Staff] report on the possibility of taking on Russia should trouble arise in our future discussions with her. We were instructed to carry out this study. The idea is of course fantastic and the chances of success quite impossible. There is no doubt that from now onwards Russia is all powerful in Europe.
He was not considering nuclear weapons, since he would not have known much about the Manhattan Project, and nobody knew how effective or practical they would be. There was lots of theory, but no more.
At some point during the 1950s he wrote an addition to this diary entry. It is a bit long to quote in full, but the salient point is:
The results of this study made it clear that the best we could hope for was to drive the Russians back to about the same line the Germans had reached. And then what? Were we to remain mobilised indefinitely to hold them there?