Michael Hirsh in een deep dive voor Foreign Policy:

“Russia has been repeatedly invaded. That’s something that’s very difficult for us in the United States to understand because we never faced a catastrophe of those dimensions,” [Thomas Graham, a former senior U.S. diplomat and Russia expert now at the Council on Foreign Relations] said. “It is a sense that goes back centuries: In order to survive, you need strategic depth, so you need to push borders out as far away from the heartland as possible—not so much physical as geopolitical barriers. You just push until you meet something that can resist you.”