This didn't last though - with taxation fixed by the elected governments various kings raised taxes by reducing the size of the gallon - this left the wine gall

This didn't last though - with taxation fixed by the elected governments various kings raised taxes by reducing the size of the gallon - this left the wine gallon (the one the US adopted) smaller than other gallons, in the 1800s the UK standardised back to the existing single imperial gallon which is why the US gallon is different from everywhere else (that whole "a pint's a pound the world around" aphorism is bogus bullshit, only true in the US)