I always find it silly how Westerners have no grasp of reunification in a non-military manner.

In the same way say, France and Germany might have a unified economy or Canada and the US might have a unified culture, it's entirely possible to maintain legislative and/or budgetary independence under a unified front. In fact, that's already more-or-less true of China's governments: the proportion of government spending at the federal level is only 15% of all government spending. This includes spending for defence, science & technology, public security, public services, education, and diplomacy.