Stop what? Russia is doing EXACTLY what we would do if an outside alliance threatened to expand anywhere in our hemisphere, let alone right on our border. And we have done this many times since the Monroe Doctrine was instituted in 1823. Russia is not going to lose its strategic -- and sole -- warm water port just because Khrushchev gave Crimea to the Ukrainian SSR back in the 1950s. Whether we or the whole world approves or not, Russia is going to secure Crimea to mainland Russia through eastern Ukraine. Ray Charles could see this coming back in February.
I'll repeat it again. There was no reasonable threat by Ukraine to Russia. None! Ukraine was NOT seeking to become a member of NATO although they have every right to do it. Ukraine was not a threat to invade Russia.
There is no justification for what Russia is doing. None!