I have written before about asymmetric conflicts and power balances in the context, among other bilateral comparatives, the U.S.-Russia military spending: http://trueeconomics.blogspot.com/2017/09/12917-asymmetric-conflicts-and-us.html. And the latest budgetary appropriations from the U.S. for 2018 are suggesting that Washington has a serious problem learning any lessons - whether these are lessons from being punched around repeatedly in the Afghanistan, or being derailed in Iraq, being made irrelevant in Syria and so on.
There is a very good op-ed from Bloomberg View by Leonid Bershidsky that is worth reading: https://www.bloomberg.com/view/articles/2017-12-14/russia-s-military-is-leaner-but-meaner. This too covers the same topic, albeit from a slightly different angle.
The article also cites our recent research on the causal relationship between the U.S. military budgets, war engagements and the valuations of the U.S. defense stocks (see here https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2975368).