According to Wikipedia,
In the People's Republic of Poland, on 8 September 1968, Ryszard Siwiec immolated himself in Warsaw during a harvest festival at the 10th-Anniversary Stadium in protest against the Warsaw Pact's invasion of Czechoslovakia and the totalitarianism of the communist government. Siwiec did not survive.
Vladimir Putin has embarked on a path of grabbing back the parts of the Soviet and Tsarist empires he thinks he can get away with. After invading Iraq, the US doesn't have the same moral authority to condemn this old-school imperialism. But the citizens of former Warsaw Pact countries do! If they organized a collective day of protest in their respective cities, could Putin be shamed?
The Russian economy relies mainly on the export of mineral resources and natural gas. Successful businesses in Russia are increasingly being taken over by the kleptocracy that rules the country. If your business model is based on theft, then to grow you need new areas to plunder.
So far, Putin is getting what he wants. In spite of international condemnation, Crimea appears to be a done deal. The provocations of the last few days suggest Eastern Ukraine is next. It is a resource-rich area and there are many native Russian speakers living there. But even many of them know that living under Russian would be no picnic. Yet they are being used as a pretext for intervention.
Kaliningrad, a Russian enclave on the Baltic Sea, has lately seen a surge in military activity, to the dismay of its neighbors. Estonia is especially concerned, because they too have a large minority of Russian nationals, and recently Russia has "signaled its concern" over its former citizens. Poland, Lithuania and Latvia have all expressed their worries about a resurgent Russian empire.
The Czechs, Slovaks and Hungarians have some especially bitter memories of Soviet tanks.
To the Kossaks from these countries and other Warsaw pact nations like Hungary and Romania: could a mass protest by all these people do anything to stop the next move by Putin?