Also, Russia cannot even take over a country which is much smaller than her, why should we hope the Kremlin to be more effective at defending their country from aliens than USA or Europe?
Russia wasn't originally trying to take over Ukraine. They were simply protecting their people and loads of Ukrainian people from Ukrainian shelling - https://bitcointalksearch.org/topic/m.61752131. They have done this by pushing the Ukraine border further into Ukraine, especially in the Donbas area.
Since it has been the US goal to conquer Russia for a long time, they simply started pouring money and military aid into Ukraine, to help Ukraine do this job for them. In other words, Russia isn't fighting Ukraine. Russia is fighting the US and Nato. The Ukrainian people simply allowed their country to get in the way.