I know they did what they had to do but they could have left Oceanside a few guns to protect themselves.
They needed the guns. They could have left a few for defense (only with the few good shots, like 3).
On the other hand, if the US was at war with another country, it would be frowned upon to just roll into a 3rd autonomous country and take all of their resources for the effort without their consent. Otherwise, you've declared war on those people, too.