All of this makes for an alarming level of uncertainty - with a 'Trumpcession' the likely result

One factor is how rival economies will respond - with retaliatory tariffs tending to make a bad situation worse

- Heather Stewart

Donald Trump is finally making good on his campaign promises to "build the wall" - but instead of steel fencing across the Mexican border, it will be constructed from tariffs, and enclose the entire United States.

In his pugnacious and typically rambling speech on the White House lawn, Trump set out plans for across-the-board import taxes, ranging from 10% to more than 40%. The president promised "liberation"; yet the immediate impact is more likely to be rising prices for US shoppers, and corrosive uncertainty for firms: exacerbating an economic slowdown some measures suggest may already be underway.

Outside the wall, countries will be affected according to how dependent their economies are on exports to the US - and how exposed they are to the global trading system. For some, it is likely to be devastating.

The precise effects of sweeping tariffs on this historic scale are very hard to predict - particularly as Trump and his team appear to have chosen a complex matrix of taxes, which will vary by country and sector.