Not even a little bit concerned. The military, from what those of us still serving can see and believe, is that attention is based on worldwide events that are encapsulated in small geographical areas and how, if we committed resources there, how it would affect the overall manpower numbers.
For example, the spurious war on terror in Afghanistan, examining future contingencies if North Korea were ever a genuine threat (they’re laughable, no matter how much they threaten and posture), possible escalating events in Africa, and the current fiasco in the Ukraine.
The powers that be have to examine the builds up’s and shortfalls of troops at home and troops abroad and also weigh the possibilities of committing even more resources to events that haven’t happened yet but could possibly arise and how that would stress out overall demands of all 4 of the service components.
If it did come to World War 3 though, with us having to face off with one nation in a large conventional type war (nukes are a complete afterthought, in my opinion, because no one wants that catastrophic event to happen anymore), it would be problematic because the U.S. military just doesn’t have the manpower levels as it did many years ago and it would be hard to amass that type of manpower needed in a short time to fight such a large conflict.