It’s all about oil. Ukraine is vital to Russia's security because of oil. The oil isn’t in Ukraine, it’s in the northern Caucasus, the first mega oil field discovered in this world and still the second largest. That’s a heck of a lot of oil, and it is only five hundred miles from the border of Ukraine. That’s too close. If NATO troops could gather on the border of Ukraine they would be well in reach of this vital prize.
This has been going on for a long time. Joe Stalin got his start in politics as a labor organizer in those oil fields. Later they were the main goal of the invading Nazis. The Reich had only the inferior Romanian field — they needed the big Russian oil. That’s why the key battle was at Stalingrad. Were the Wehrmacht to drive rashly to the oil fields the Russian divisions near Stalingrad could cut them off. To get the oil safely the Germans had to deal with the menacing troops near Stalingrad. They tried.
It took the Nazis two years to fight their way across Ukraine. If they instead had been able to start at the eastern border with Russia they surely would have taken the oil fields. Then they would have ample diesel to fuel their big modern armies. Russia would have been short of fuel and in deep, dark trouble. In short, if the Nazis had been able to start in eastern Ukraine with only five hundred miles to the center of the oil fields I believe they would have won World War II. This is why a neutral Ukraine is vital for Russia. Ukraine going NATO would be a huge blow to their national security.
Back when the USSR collapsed the Russians lost direct control of the Baku oil. Then the region of Chechnya broke loose. You ain’t leavin’ buddy.