In WWI 1914, the only retreats allowed are with sea battles, and retreating units simply remain where they are and the battle ends. Add a new game property that allows retreating to the battle site and disallows retreating to an adjacent area.
I dislike having the logic be in attackerRetreat(), because it should be in getAttackerRetreatTerritories(). Other functions call this, and we should know that there is only 1 territory and that it is the battle site.
I moved the logic to getAttackerRetreatTerritories() and have committed.