Well...that's pretty much the case. Valhall recently had a civil war (War of Princes) and was completely united. The Emperor desires a certain World Domination. So either he wants a nation to become his ally (so he can slowely but surely take it over through installing a few of his own guys) or declare war on you. Also, it sort of depends on who you are. For example, if you have a huge nation, he won't be willing to attack you immediatly. Valhall would try to become allies and the turn the nation. On the other hand, if you're too small, they won't really care and just invade you. Unless of course, your people have some unique ability (like Dracanica's dragons). Of course, at first everyone just receives a letter in which states that they can either surrender, become an ally or declare war on Valhall.

As for what has happened so far. Several hundred envoys have been send around the world with the letters, giving it to rulers everywhere. Dracanica has already declared it's allegance but Lacria refused. Dracanica's envoy is now on it's way towards Lacria because of it's mysterious passed with the Dragons. But does this under cover of diplomatic negotiations.

And yes, you can put your nation sheet up.