The bases in Germany were certainly "necessary" after WWII, but 70 years later, do we still need so many and do they need to have so many personnel? Especially with all the "force multiplying" technology that's been developed since WWII.
We definitely need to revisit how much of this is "necessary" today. I will say this though, for the populace in Japan/South Korea/Eastern European countries, the necessity of the nuclear umbrella is not theoretical vis a vis China (in Asia Pacific) and Russia (in Eurasia, particularly after the events in Georgia a few years ago)