Western invasion of "Russia" predates 1812, by a little bit. Russia as a political entity didn't exist, but the culture extends back. The Teutonic Order famously invaded "Russia", along with Lithuania, Poland, the PLC, Sweden.
Everyone in Europe has been invaded at one point or another, but "Russia" has never really been apart of Europe, not really. It's like in grade school, "Russia" historically has been the kid it is socially acceptable to pick on. However it goes beyond that, Russia in the last few centuries has suffered from these invasions like no other country in history has.
You are confusing the vaguely formed entity of Kievan Rus with modern "Russia". And lots of countries have suffered devastating invasions - the German lands for example in 1618-1648 suffered far more than Russia ever did before 1941. Poland likewise suffered far greater deprivations between 1650 and 1790. Hungary and most of SE Europe has also been subject to prolonged subjugation since the onset of the Ottoman invasions.
I do not subscribe to the idea that Russia really played into starting WW1. I support the idea that Germany hijacked the Austro-Hungarian war as a way to pick a fight with Russia while Germany was still he most dominant European land power. Basically it was a way for Germany to knock Russia down which was on course to surpass them at the dominant European power.
No, Serbia was Russia's cat's paw. And it still is to some extent.
In anycase, the losses they took in the 19th century invasions, and then the 20 century invasions are incomprehensible. They are unreal numbers. I'd challenge you to show me any country on Earth that would sit back after being invaded twice in a century to the tune of tens of millions of dead and not take a pro-active stance to creating buffers.
It's wrong, but it's easy for us to cast judgement. I can also totally understand why this would radicalize their foreign policy.