Semi-seriously: Ukraine at least had a treaty securing its borders by the US, UK, and Russia. If the US and UK aren't willing to act on that treaty, what makes one think they'd act on a NATO Article V invocation by them if they were NATO members?
Domestic European squabble developed into bloodiest conflicts the world had seen, more than once, never mind whole continents in submission and despair up until the 50s. Yet it is Russia that poses perpetual imminent threat.
Very unfortunately for territories bordering Russia, they are a, indeed, a buffer zone and get mowed down and/or change hands every time shit hits the fan. Equally so, in fact, by Russia and by the Western (“Proper”) Europe.
The soft power Russia has seems to be growing, never mind the wars they are all too happy to fight without acknowledging that a war is being waged.
Meanwhile Europe is diversifying its sources of fuels, so it seems that they will lose any ability to do that eventually.
AFAIK, the same reason holds for Syria: to stop Qatar attempt to reach Europe.
Two world wars happened since at least 20th century. Napoleonic before that.
Countries go to wars. Since forever. Aggressively and recklessly. Doesn't make agreements less important. A poor agreement is better than a good war, isn't it?
I think your understanding of History is flawed at best.
Also, haven't seen Sweden invade anyone recently.
and historically, everyone surrounding russia has been trying to limit, constrain, or invade it (eastern crusades, crimean war, western sponsorship of lenin, etc).. what is your point?