It's Greece-Turkey, as others have said. Turkey has burned through much of it's foreign reserves, tourism is fucked and we could see Erdogan whipping up nationalist sentiment in the face of major economic difficulties.

Longer term, as Putin slides out of the picture with his medical issues, Russia is an interesting candidate for instability. The Chinese might try to solidify their land grab in the east, but the bigger worry is Russia breaking apart and imploding.

Europe has zero capability for warfare in the Pacific, so that is irrelevant.