There's US state taxes (for those states that have it), which does not get credited with foreign income tax. There's a lot of VAT (value added tax, aka sales t

There's US state taxes (for those states that have it), which does not get credited with foreign income tax. There's a lot of VAT (value added tax, aka sales tax) that gets paid when buying goods. If this was higher than the US's in the expat's country, they don't get a credit (but conversely, if it was cheaper, then they also don't have to backpay...).