I think because they needed to get the upper hand in the war before the other side did
The NW ordinance of 1785 is what your looking for I think
The two possible outcomes are:
1. The boomtown losses it's economic power, and people migrate away from it to other places that they consider better for living, and thus leaving it as a ghost town.
2. After the main income of the boomtown is lost, people put their efforts into other things that can make them survive and keep the town alive, maybe a timber industry, fishing, agriculture, tourism.