Ukraine's oil drilling concessions to Western supermajors and its gas pipelines to Europe are very attractive assets. Russian forces are likely to seize those assets if they enter Ukraine under the guise of peacekeeping. Russia's state-sponsored energy companies act as arms of its national grand strategy. President Putin and his allies in the Russian deep state desire more than a recreation of the 18th Century Novorossiya. They covet Ukraine's assets as compensation for the payments Ukraine has been unable to make on its debts. Ukraine's own deep state elites, aka its nationalist oligarchs, got a little too greedy after many years. Now it's time to pay the piper.
Nation-states don't look like debt-collection rackets in history books but Americans never had the patience to read much history. That's why Russia's aggression in the Donbas takes so many Americans by surprise. Lower-class Americans only experience the repo man when he comes for their automobile after they can't make car loan payments anymore. Transnational repossessions happen when strong nations want their weaker neighbors to pay their debts.