Yes, the war actually started with both Germany AND Russia invading Poland.
No, Germany haven't invaded the rest of Europe, in case you've forgot, both Britain and France declared war against Poland invaders (though not on Russia..), so actually Germany was in a state of war with France and Britain.. so, that's not an invasion (as in we've invaded them over night), but a legit part of the war actions.
Yet.. DO you know about this little declaration?!! Read it carefully please, and go dig it into the war magazines archives in case you think it's forged:
"
Poland wants war with Germany and Germany will not be able to avoid it even if she wants to." (Polish Marshal Rydz-Smigly as reported in the Daily Mail, August 6th, 1939)
What if actually Poland was acting as the small thug, knowing it has binding treaties with other two BIG thugs (read France and Britain) to jump in for it, no matter what?!!
There are voices saying that actually Poland was salying german population from the german territories taken from Germany and given to Poland at the end of WWI, and that was actually the reason for which Germany invaded Poland.. read
Polish Atrocities Against the German Minority in Poland, and read it full, not just the main article in there
Things are much more complicated than they are presented to us by "official history"..