As others stated, having a "towny war" between nations (that cost 5 million skulls) seems pretty impractical. Although the whole idea of different towns unified to a nation is designed for a towny war, the current economy is only capable of two nations (currently 13 mil+ skulls). What if nations can start with say, two towns agreeing to team together and pay off a 1 million skulls fee (each). Then once that "nation" is built, other towns can further join in that nation with higher incremental fees. This idea allows for nations to actually be made while limiting nation sizes to become "too op" based on size.
As example:
1. Say two towns require 1 million each to start a nation
2. Another town wants to be a part of that nation requires 2 million to participate... and so forth.