North Korea is contained, China has legitimate territorial disputes with its SE Asian neighbors and Japan (diplomacy and economics is the first line of defense with China.), Iran can also be dealt with within the existing defense budget.  Now, if you see some type of aggressive alliance forming with these nations, I'm with you.

Our real threats are massive human displacements for various reasons; climate change, overpopulation, no economic growth or reversal, disease, etc.  The way to deal with those is to secure/control our borders, start training our kids/work force for the jobs that will be needed, ensure we have the industrial capacity to build whatever is needed, access to raw materials, innovative technology development, and national unification.