Add terrain features to the maps, like mountains, deserts, rivers, etc., that modify the defense when attacked. For example, if a region is mountainous, an attack will either be cut in half or the defense will be doubled (just for the duration of the attack). A river on the border of a region may increase the defense by 10% or something. A desert may reduce the defense (no place to hide).
Add terrain features to the maps, like mountains, deserts, rivers, etc., that modify the defense when attacked. For example, if a region is mountainous, an attack will either be cut in half or the defense will be doubled (just for the duration of the attack). A river on the border of a region may increase the defense by 10% or something. A desert may reduce the defense (no place to hide).