Edward Luce’s warning that the global role of the US dollar will become unhinged by a debt shock (Opinion, May 31) joins a rising chorus of justifiable concern about where President Donald Trump’s America is headed. This warning, however, seems incomplete in its focus.

Remember the UK’s public debt as a share of GDP was continuously between 100-250 per cent from 1750 to 1850, and again in the first half of the 20th century. Sterling’s reserve currency role, still dominant in 1940, was undermined by two global wars during which it borrowed heavily from the US, and was torpedoed not by debt but by the UK’s loss of economic pre-eminence. Suez marked the point where the reserves held by Overseas Sterling Area countries were finally swapped for dollars, but the UK’s loss of economic resilience, colonies, military power and other attributes of global hegemony were decisive.

The US could follow suit in some respects. Yet it enjoys considerable advantages, not the least of which are its military and security status, and Mr Trump notwithstanding, its technology and soft power. The dollar still accounts for over 63 per cent of official reserves, more than three times as much as the euro, the future of which is, shall we say, uncertain, but likely to be secondary to the dollar. The renminbi’s share was a mere 1 per cent. Whatever happens to China’s economy — and it is also no debtor slouch — its structural balance of payments position and capital controls preclude the renminbi from becoming a more important global currency.