It won't work, many reasons why but I'll state a few big ones.
First, many many nations raid so who we they all raid.
Second, let them build for 30 days and everyone else war, they would become the superpower.
Third, Who's to say other people wouldn't join and build only to leave and form an alliance or Rouge other alliances.
I can keep going with this but those 3 alone should be enough to get people to see any it wouldn't work.