As the crisis escalates over Ukraine, it has become increasingly clear that not only the rebel leaders but also most of their 15,000 fighters are Russian citizens. The Ukrainian troops are far more numerous with 40,000 to 60,000 men and demonstrate much better morale. They have recaptured three-quarters of the territory formerly controlled by the Russian insurgents. The Russian-held area has now shrunk to an area where 2 million people used to live. Even so, the West continues to favor a political solution to avert an outright Russian invasion, presuming it would end in a Russian occupation of the country’s east.

Yet an outright Russian offensive is far from certain to succeed. To understand why, it is worth reviewing an obscure episode of history, the Soviet-Finnish Winter War in 1939–40, which lasted just over 100 days. The Finns amazed everybody and prevailed over Stalin. The Ukrainians can do even better with President Vladimir Putin.