This is their stated initiation, but they're taking airports just outside of Kiev at this point. Might be the goal is to quickly crush the Ukrainian military and force capitulation to all of Russia's demands, e.g. formal recognition of the two breakaway regions as independent nations, similar to what happened in Georgia in 2008. Or maybe it's full blown depose-the-government and install a puppet, and have "peacekeeping" forces stick around for a good long while.