Fort Rucker in the USA, and the surrounding 5 airfields, has the highest concentration of (at least western-world) military helicopters used for training. Around 600 helicopters at most times, plus a mix of other aircraft. Most of the surrounding airspace is designated as an "Alert Area".
This is a link to the
VFR Chart. Here is a link to the definition of
Alert Area.
It may be that military helicopter pilots and the pilots of associated supporting fixed wing aircraft in the USA are able to deal with the stress of the possibility that there may be random, unidentified Cessna 172s and equivalent threats in the air with them. One wonders how they've managed to survive as a super power.