[gressquel]

I think Japan, Germany and South Korea prefers to "lease" US military as they're doing now rather than having their own military as the sole defence for the country. Germany in particular has shown signs of enjoyment in such an arrangement, leaving them to focus on other issues like building their economy and commanding EU. There is a reason why Trump is demanding more commitment from other NATO countries. An analogy to computer game would be, US is defending the NATO countries (+japan og SK) while the others are focusing on 'booming'.

If one day germany, japan or south korea were to decide to have referendum to remove US troops and get majority vote, I am sure US would remove their troops. So in short: no, US is not holding a gun to them because the other countries are certainly enjoying US nuclear and military umbrella protecting their territory.