@jansenpapworth , depends on your immigration and Tax status ---- If you here on a work visa , till you pass SPT ( Substantial Presence Test ) or request to be treated as a resident , you are taxed on US sourced income. Thereafter you will taxed by the US on world income ( including any gains from alienation of assets anywhere in the world ).
Any Taxes paid to a foreign taxing authority (/ ies) is eligible to Foreign Tax Credit.
Does this make sense ?
Is there more I can do for you ?