From the White House Rose Garden, President Trump called it “Liberation Day” for the United States, but in garment factories in Hanoi and Phnom Penh, the announcement of his “reciprocal tariffs” arrived like a declaration of economic war.

For more than seven decades, many countries have followed the same path out of poverty: make things, and sell them abroad. This strategy, known as “export-oriented industrialization,” was rooted in domestic reforms but turbocharged by the opening of the world economy under American leadership after the Second World War.

Mr. Trump hasn’t just brought this opening to a crashing halt — he has raised trade barriers not seen since the Great Depression. Vietnam and Cambodia will now face punitive tariffs of 46 and 49 percent on exports to the American market. This is a profound shock since these sales account for around a third of their G.D.P.s.

Policymakers and investors in countries that have bet their futures on international trade are right to fear the consequences of America’s protectionist turn. But the truth is that their strategy had been running out of steam for decades and was no longer delivering for most developing nations. To reignite growth, these nations will need to tune out Mr. Trump’s trade antics and focus on the deeper challenges they face: developing their home markets, their middle class and their service sectors to create decent jobs.

The model for poor countries hoping to grow rich was pioneered by the four Asian Tigers: Taiwan, South Korea, Hong Kong and Singapore. In the 1950s, they were about as poor as African nations and heavily dependent on agricultural products and raw minerals. Trade allowed them to specialize in increasingly sophisticated manufactured goods for sale on world markets — toys, clothes, steel, cars, electronics and now semiconductors — while providing them with access to advanced technologies and machinery.

China soon followed suit, perfecting that strategy to become the world’s manufacturing powerhouse, lifting 800 million people out of extreme poverty and emerging as America’s chief rival. (China’s strategy may have worked too well: By the time Joe Biden became president, “beating” China had become a bipartisan imperative.)

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