In light of the large army, it is highly unlikely that the movements to and from Bethel involved the whole military force. Most likely, it was the leaders as representatives who went up to Bethel. Judges 20:26, which says that all the people of Israel, the whole army, went up,
is the exception.1
18 The people of Israel arose and went up to Bethel and inquired of God, “Who shall go up first for us to fight against the people of Benjamin?” And the LORD said, “Judah shall go up first.”