9. The Russian Revolution: 1917
Now, the Russian Revolution is a complicated affair. Tsar Nicholas II's rule was tyrannical and outdated, and brought about horrendous casualties in the First World War. He was forced to abdicate in February 1917, and a provisional government took over, but this was effectively useless. Then Vladmir Lenin's Bolsheviks staged another coup in October, forming the USSR and abandoning the war. But even before Joseph Stalin took over, the new communist state resorted to violence and terror to suppress opposition from reactionaries and other leftist movements, causing more deaths than Adolf Hitler. The complexity of the Revolution is the most appealing aspect. It is one historical event that cannot be addressed with any form of bias, as no side could truly claim the moral high ground. A potential episode could fall into the 'some-events-cannot-be-prevented' category, maybe with the Doctor and his companion meeting a really nice Tsarist soldier who's doomed to die or a cool Bolshevik who helps them fight the monster, but is destined to turn into one of Stalin's murdering psychopaths. Good and evil factor into Doctor Who a lot, and a trip to Revolutionary Russia would be a good opportunity to examine the blurred line inbetween.