"...the first 1917 revolution gave Kerensky the opportunity to establish his powerbase"

Actually I'd thought of saying something close to that, but significantly different, and pointing out that people who backed Lenin arguably carried some responsibility for Stalin's rise to power from his base in Lenin's party.

There were all kinds of reasons for Hitler getting control, but one of them undoubtedly was people thinking in terms of "my enemy's enemy is my friend" - and not looking too closely at who some of his enemies actually were. And that was certainly the case with Saddam and Bin Laden more recently, and explains the backing they had from people who would rather that this was forgotten. (Of course this is a way of thinking that occurs among left-wingers every bit as much as on the right.)

And I said nothing about anything being inevitable.