The Nephites did not have a standing army. There was generally no such thing in the ancient world. When a nation went to war, the farmers had to leave their plows and their fields. They knew where to gather, because a commander would walk around the town or the land holding a pole up in the air. This was a traditional signal to come report for battle. I recall reading a brief account in Roland de Vaux’s impressive work, Ancient Israel, about a group of surveyors who were mapping the hill country in Palestine a century ago. The put their sighting picket on the top of a hill and then were unnerved to see the local men charging up the hill asking, “Where’s the battle?” Captain Moroni evidently knew of this ancient tradition as well, for the thing that brought the people running with their weapons was the “pole” (mentioned in 46:12–13). The covenantal declaration on this piece of cloth, not the pole, was the innovative thing. Captain Moroni then also ran a good public relations campaign, as he placed those words on similar banners on the walls and towers of the Nephite cities.
Kerry Hull, “War Banners: A Mesoamerican Context for the Title of Liberty,” Journal of Book of Mormon Studies 24 (2015): 84–118.