US President Donald Trump has warned that America could become a “third world nation” if his tariff policies are overturned, after a federal appeals court ruled most of them unlawful.

Trump introduced the tariffs in April, accusing trade partners of exploiting the United States and imposing rates between 10% and 41% starting August 7. He defended the measures as a way to attract investment, revive domestic manufacturing, and secure fairer trade terms.

However, the US Court of Appeals for the Federal Circuit ruled that Trump exceeded his authority by imposing the tariffs under an emergency-powers statute, noting that only Congress can approve such measures. The court did not immediately cancel the tariffs but gave the administration until mid-October to appeal to the Supreme Court.

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Reacting to the decision, Trump wrote on Truth Social that more than $15 trillion in investment was tied to his tariff policy and warned that it would be “immediately cancelled” if the ruling stands. He argued that removing tariffs would destroy economic momentum and reduce the United States to “third world nation” status.

The decision affects Trump’s broad “reciprocal” tariffs on most trade partners and specific duties on goods from Canada, China, and Mexico tied to drug trafficking allegations. It does not apply to targeted tariffs on steel, aluminum, and automobiles, which were enacted under separate legal provisions.

Economists remain divided on the impact of tariffs, with critics cautioning that they risk slowing growth and increasing the chances of a recession. Trump has also threatened additional tariffs on India and China while warning of sanctions on Ukraine if the conflict continues.