The US Empire is capitalist in Smith's sense, though. The US still operates on commodity circulation, private ownership of capital, etc. Smith was just wrong in thinking the invisible hand would fix everything (along with other issues like the way he categorized fixed and circulating capital being a step back from Quesnay and the physiocrats).
The "protectionist oligarchy" was in capitalism from the beginning of its formation, what's important to recognize is that systems grow and change through their own compulsions and contradictions. Capitalism necessarily centralizes and expands over time, and the state exists to keep that system going.