An army with the Purge the Foe Force Disposition facing one with Take and Hold is dealt Unstoppable Force as its primary mission.
The opposing army is not playing the same mission: it is dealt Immovable Object. Reading only your own card is how a game gets lost from in front.
Purge-the-Foe against Take-and-Hold. Destroying any enemy unit pays at end of turn. From the second battle round, per-objective non-home control pays at the end of your Command phase, with a separate end-of-turn payout for seizing non-home objectives you did not control at the start of the turn. End of battle rewards holding a central objective.
Primary scoring is capped at 15 victory points in a battle round and 45 across the game.