That stretches it a bit. If a foreign base in your country makes you a protectorate, the USA is a protectorate of Germany (http://en.wikipedia.org/wiki/Holloman_Air_Force_Base#German_...)
In other words: one should nuance that a bit. Yes, in NATO, he USA is by far the biggest player, and it contributes beyond its size, but protectorate stretches it, certainly in some cases.
63 countries have US military bases and troops, 156 countries have US troops (overlapping sets), 46 have no US military presence[0]. The Five Eyes are basically the US's subalterns in Empire. Outside of Russia , North Korea and China calling non US countries independent is a bit of a stretch. Classical international law certainly wouldn't have considered any country with another's military bases anything but a protectorate.
[0]www.miprox.de/USA_speziell/US-Military-Bases-Worldwide. jpg