A million people marching through London. Impressive. Even at the peak of the reform movement in Russia, in the late 1980s, the largest gatherings in Moscow totaled 500,000 [up to a million probably – added in July 2017] people or so. And the Soviet Union was then roughly equal to the US by population.
But then, many of yesterday’s marchers came from other parts of the country. That can’t be done overnight in Russia — a country so spread out that it takes seven days to travel from the Far East to Moscow by train; and air travel wasn’t cheap then (nor is it now). To mobilize large groups from the Urals and Siberian cities would take a lot of time and money. Obviously, no level of support for reform could make hundreds of thousands sacrifice a month’s worth of candy and butter for a plane ticket. The protesting crowds in the Manezh square consisted mostly of Muscovites — and a turnout of 0.5 million was not bad for a city of 8 or 9 million.