To have an account in the US Store you must be a legal resident of the US, provide a credit card issued by a bank in the US*, that has a verifiable billing address in the US.
*Or redeem a US iTunes Gift Card.
Late 2012 Mac mini, macOS ?; Watch, 38 mm silver AL, Watch OS 2.2.1; iPad Air 2 & iPhone 6+, iOS ?; Apple Airport Express