He opposed it because he wanted to keep the union together at all costs. During the civil war for example he went to war with the south in order to preserve the union.
I know it's short but hey it's something.
Barbarous,destructive,vandal,offensive, and disparaging
The balance of power, depended on its effectiveness upon clearly defined, centrally controlled, independent entities, whether empires or nation states, which recognize each others sovereignty and territory