那

A distant city or state's name in ancient China. That one, the far one — a pronoun pointing to something not near. The 阝 (mound) on the left marks a remote spot; the right side looks like a hand pointing "that over there.

那 in the dialogue, reaching back to a given condition to move forward. Then; in that case; so — a quick pivot from a premise to its result. A flag (冉) raised over the town (阝) marks the turning point: from there, "then" follows.