You have to pick a nation. Remember, your choise is final. Hereafter you won't be able to pick the other nation. Think before you act.
It might be the case a nation has way to many players around your level at a certain moment. For balance reasons, you won't be able to enter that said nation. Either you'll have to wait until a later moment (until you can join the nation you wanted to join), or you should pick the other nation.
Once you started this mission, you can't cancel it anymore. You'll be permanently promped to choose a nation.
