Who do I directly threaten? I have only attacked Rus once and that was due to the fear of a mighty Hungarian-Russian alliance. My worst fears have been realized it seems. Yes, I have fought player realms, but that's because I have nothing else to fight. I am completely and totally surrounded by player realms. Hungary in the south, Rus in the east, Norway in the North, Brandenburg and Bavaria in the west. I've had no choice but to expand considering that Rus and Hungary alone command 40-50k more troops than I do. What else can I do?! Watch Rus and Hungary grow and grow while I sit back and do nothing? Also, please don't forget, I have used my power to bring stability to the region in past years. I saved Hungary from a massive rebellion that nearly tore it apart. I saved Naples from absolute destruction by the heathen hordes. I saved Brandenburg from re-incorporation into the HRE.
Then there is the matter of lands I've released. I could have a chance against a Russian-Hungarian alliance if I had not released Georgia. Hungary has given up about three provinces, all worthless, and that is all he has ever released. I've given up nearly two dozen provinces to KoG and KoJ. Had I kept those, I could at least hold my own against the barbarians east and south.
Simply realize, Rus and Hungary could take me on alone. They have far more troops than me and I have just fought a rather large war. These two powers allied are unstoppable. Castille and Naples couldn't bring them down, maybe if Byz and Norway joined in they could. But basically... Poland has had to attack humans because there's nowhere else for it to expand and there normally would be no need except for the expansion of the Hungarians.