Tsar Nicholas II abdicates his throne in the wake of the "February Revolution" in Russia (February in the Julian calendar still in use in Russia at this time, March in the Gregorian calendar used in most of the rest of the world, including Europe). Nicholas II intends another member of his family to take over, but the revolutionary uprising in Russia cannot be halted and the Romanov dynasty comes to a end.
Nicholas II hopes to go into exile in Great Britain, but his cousin King George V forbids this out of concern that his presence will create problems. Had Nicholas instituted even modest democratic reforms like those he saw in operation in Britain, he might have been able to avoid revolution in Russia. It's not clear that the Bolsheviks would allow him to leave Russian anyway and the family is held in captivity until they are all murdered in July, 1918.