It is beyond me to understand how Putin allows the wholesale slaughter of ethnic Russians in East Ukraine.
The video below shows an artillery shell whizzing by and slamming into what looks like a residential area of Donetsk. (H/T Zerohedge.)
(You can see the shell whiz by at around 1:37 in the video.)
Back in 1983 the United States sent the full force of its military to invade the tiny Caribbean island of Grenada on the trumped up reason that American students were in danger there after a coup.
Putin is clearly afraid of US reprisals. Maybe he fears more sanctions. Despite mainstream Western media and neocon propaganda and assertions to the contrary, he's been largely pacified.