Split the Nordic peninsula into 3 countries, but borders run east-west. People in former Finland have to go through another country to get around the Gulf of Bothnia / Baltic Sea.
Expand borders of Germany, you know, just so they can have some Lebensraum. There won’t be any issues with that surely.
Balkan superstate. Make sure everyone has a voice in its vibrant democracy, but gerrymander the hell out of it.
Merge southern France, Spain and Italy so the merged country can have maximum Mediterranean beachfront. Just think of the tourism revenues!
Suggestions for maximum chaos and discord:
Yugobosia