Nikolai II was unprepared to be the Tsar. Why?

Because he knew nothing of military strategy or of running Russia economically

I agree with Pavlov that Nicholas and Alexandra were not suited by personality to be rulers of a country such as Russia. In that sense, they contributed to the start of the Revolution; however, there were other factors at work, because the forces that led to the Revolution happening had been developing for years in Russia, long before the birth of Nicholas II, even. So these factors seem to have been more at work than Alexandra's personality and actions in causing the Revolution. Also, Queen Mary, King George V and the British royal family were constituentional monarchs, it must be kept in mind, which is rather different than being an autocrat like Nicholas II was, or an autocrat's consort, as Alexandra was. I think Nicholas would have made an excellant constitutional monarch, but he wasn't suited to be an autocrat. So the difference that the Romanovs, especially Nicholas and Alexandra had a lot of power, whereas the British royal family actually had very little power must be borne in mind, although it's true that Alexandra's personality and attitude was likely not suited to even being the consort of a constituentional monarch, and also Nicholas II was not a good autocrat.