Its not really that surprising. The relationship between Russia and the Ukraine is similar to that between Britain and Ireland. They were ruled over for centurys and poorly treated, even suffering famines. The Ukrainians have built up a terrible hatred for Russia, but they never had a chance to properly express it. Now, they see their chance to finally settle old scores.

Besides that, the Ukrainians display the same hyper-nationalistic traits found among the Polish. They would fight even if they were being invaded by a nation less hated than Russia. The Ukrainians were denied nationhood for many centurys []; now that they have their own country, they have no intention of letting it fall to the old nemesis.

[] Even during the era of the Soviet Union, they were not a true nation, merely a republic with very little autonomy.