Has it's own version of everything, physically segmented, even for global systems such as IAM.
You have to be a US Citizen to work on it and you need special security clearances.
GovCloud customers only need be a US person or entity, beyond that any further regulatory alignment is up to the customer. AWS does not audit the IAM user base for nationality or any compliance requirements.
Disclaimer: I am an AWS Public Sector Solutions Architect.
[0] - https://aws.amazon.com/about-aws/global-infrastructure/regio...
GovCloud I believe is technically separated in this regard, I don't think IAM credentials can operate across partitions.
Though it does seem to be possible to link the existence of a standard AWS account with GovCloud, the same is not true of the China partition