I think that Ukraine was deeply weakened by the fall of the Soviet Union because of the aid (however crappy it was) that they got from the USSR. It had backed them up for most of the 20th century and when you have been a puppet for your whole life it is a little hard to all of a sudden be in charge of yourself. But when you have been under the cruel dictatorship for almost 100 years it would be nice to be free. So when Russia marched in they were not happy to see them. The people were already in a bad mood from suffering famine so like Russia itself it got violent.