In 1945, I don't think there was any intent to have representation of "the whole world" on the Security Council. The concept of the UN was crafted when many people believed the grand alliance of Britain, the USA, and the USSR might become permanent...and the Security Council would ensure that nothing would happen in the postwar world that any one of these three would oppose. China and France were eventually added (as noted by others) to be in part safe surrogates of the US and Soviet interests in Asia against any resurgent Japan (China) and Britain against any German resurgence(France). Of course all of this naïve hopefulness fell apart as soon as the war was over.
As others have said Stalin, in particular, opposed any SC membership from from the British Commonwealth or from Latin America because he presumed they would be stooges for Britain and the US, respectively. In 1945, this was a very realistic, if ultimately incorrect, assessment.
But the key point remains: The Security Council is the enforcement arm of the UN and SC members must have substantial and far-reaching military power and, most importantly, a veto over any SC resolutions to ensure that the UN itself does not take any action that might lead to war among them. It was intended to be a select club, not a representative body...that's what the General Assembly is.
