Q - The international norm is that double tax relief (ie the permissibility of treating foreign tax as if it were paid in one's home jurisdiction, so deducting it from a local tax liability) will only apply if there is a double tax treaty (a) between the two tax jurisdictions and (b) recognising the foreign tax in question as to be treated on account of the local tax in questions and (c) all the relevant forms are correctly filled in. Something has gone wrong with my grammar there but you get the point.

The US does not (I am sure) have double tax (or multilateral tax) treaties with the whole world.