At what point could someone have foreseen the invasion of Ukraine? Could it have been planned from the beginning of the denuclearization of Ukraine? Back in 1993 University of Chicago professor John Mearsheimer predicted aggression from Russia towards Ukraine if the denuclearization would happen.
Am I crazy, or is this way too farfetched that someone planned the coming isolation of Russia with all of these sanctions and the possible fall of the Russian Oligarchy?
The USA was instrumental in orchestrating the denuclearization through providing funding, negotiation skills, and technical prowess is denuclearizing the three countries. However, according to The Origins of Nunn-Lugar and Cooperative Threat Reduction by Paul Bernstein and Jason Wood, all parties -- Ukraine, Belarus, Kazakhstan, Russia, and the USA -- were in favor of denuclearization of Ukraine. Disregarding the political reasonings for denuclearizing, the fear of instability and therefore further proliferation, as well as the difficulty in establishing de facto control by Ukraine, from a technical standpoint keeping Ukraine nuclear-armed -- especially in a stance equally designed to threaten Russia and the West -- would have required near complete reconstruction of the nuclear arsenal. The weapons were ICBMs, not designed to be used against a target the next nation over. Reconfiguring it to even threaten Russia would have been difficult (and who know if Russia would have tolerated it).
If nothing was done, then Ukraine, Belarus, and Kazakhstan probably would have had to try to claim Nuclear-Weapon State status (i.e., international legally-recognized allowed Nuclear-Weapon State, in contrast to the illegal Nuclear-Armed State). That would have invited retaliatory measures by any number of countries as well as soured relationships between the Nuclear-Armed States -- many of which were and still are today trying to achieve Nuclear-Weapon State status -- and the P5 (e.g., the Nuclear-Weapon States).
However, your question brings up other points regarding history. The danger with looking to the past in an attempt to foresee the invasion of Ukraine is that we adopt a teleological lens. This results in a presentism which strips the past of identifying characteristics, ideologies, epistemes, and emotions. This is not to say there is no merit in attempting to see historical causes for present events, only that we should do so cautiously. Determining which forecasts were true due to a great insight or due to sheer coincidence is difficult.
Schultz and Goodby, ed., The War that Must Never be Fought
Ariel Levite, Never Say Never Again: Nuclear Reversal Revisited
Paul Bernstein and Jason Wood, The Origins of Nunn-Lugar and
Cooperative Threat Reduction