Wasn't the whole point of the post-WWII system that countries weren't allowed to grab some (or all) of other countries' territory? It didn't always work: the Russians annexed Königsberg, the Chinese grabbed some territory from India's northern border, the Azerbaijanis tossed out their Armenian population and took their land, and so forth. In general, though, the principle was respected: just look at the long negotiations over the status of Hong Kong or Timor-Leste or the former Yugoslavia. Perhaps the international community will be able to prevent Vladimir Putin from adding more territory to what is already the largest nation on the face of the earth, perhaps not. But rewarding the use of force, whether that force is used by powerful nation states or criminal gangs like Hamas, may take us down a very dangerous road.