The Palace does not count as one of the 2 national wonders. The Forbidden Palace DOES count as one of the 2 national wonders.
You mean the promotion? It gives you a certain bonus withdrawal chance. So, for instance, if you have Flanking I and II promotions on a Horseman, that'll add a 30% withdrawal chance to get a total of a 50% withdrawal chance. So when you go into battle with that Horseman, if you have (say) a 60% chance of winning, you'll also get a bonus 20% chance of withdrawal (half of the remaining 40%)... so you have 80% odds of your Horseman surviving the attack.
Not sure if it's what you were asking for, but hope this helps.