Normally by "jamming" they mean broadcasting noise that downs out the GPS signal. It's a lot more technically difficult to "spoof" the signal and would require transmitters throughout the region, or control of the satellites themselves. Of course the US military has both of those things, but I'd still expect jamming rather than spoofing.

Would jamming GPS also render GLONASS or Galileo unusable?

They're similar but separate. You could jam just GPS, or you could jam all three and still call it in common speech as "jamming GPS".

There's no chance the U.S. military doesn't have the ability to selectively knock GPS out nation-wide. Odds are the American government has infrastructure in place to do the same in dozens of countries worldwide. GPS would never have been made available to the consumer market without this level of absolute control having been put into place.

It's frightening to see how casually the American government takes disrupting GPS. The fact is, there is risk in performing these tests near civilian populations. It takes one pilot - or someone else who depends heavily on GPS - to make a fatal mistake. It's not physically necessary to black out GPS for training... just take away the trainees' hardware, or program the firmware/software to act in the desired way. "How do we train our troops not to rely on GPS? I guess the only way is to disrupt GPS for a thousand miles around the training site!"

I think these tests should happen military excersizes or not. In fact turn the entire constellation off for 24 hours at random periods once every few years or so.

The over reliance on the GPS system is downright scary, and I doubt we even have a real idea of where the second-order effects lie. What happens when all the CDMA towers lose clock sync? Are airmen still able to actually navigate? Etc. etc.

Civilian preparedness needs to be part of national security "training" as well - and GPS is one of the largest vulnerabilities we have as a nation no one talks about.

One second-order effect would be large number of people that would be unable to leave their house and make it to the local grocery without the use of GPS. It never ceases to amaze me how many people that I will ride with to go somewhere local, yet they will insist on using the nav system.

I use my nav system for the live traffic updates not because I can't navigate to a nearby address by reading street signs.

The era of self driving cars will be fun when GPS goes down

Though if you get GLONASS and Galileo you could compare and see if one is all of the sudden off?

Of course if they are faking GPS, they'll probably get the capability to fake the others.