President Donald Trump on Wednesday signed the new USMCA North American trade pact with Canada and Mexico into law, pronouncing a "glorious future" for US industry.

The USMCA, crafted over years of negotiation between the three countries, replaces the 1994 North American Free Trade Agreement, or NAFTA.

Trump has long campaigned against NAFTA, which he said resulted in shipping US jobs abroad.

"Today, we are finally ending the NAFTA nightmare," he said at the new treaty's signing ceremony in the White House.

Analysts say USMCA retains many elements of NAFTA, a mammoth deal that created a free trade zone across all of North America, shaking up entire industries and supply chains.

Economists say that overall NAFTA increased growth and raised the standard of living in North America, binding the three countries in a complex web of trade rules and services.

But the new deal does change content rules on auto manufacturing, to boost US jobs, and requires higher salaries for some Mexican auto workers.

US President Donald Trump signs the United States - Mexico -Canada Trade Agreement, known as USMCA
US President Donald Trump signs the United States - Mexico -Canada Trade Agreement, known as USMCA AFP / SAUL LOEB

It also makes changes to e-commerce, intellectual property protections and dispute settlement for investors, as well as imposing tougher labor provisions, requiring reforms to Mexico's laws.

Mexico ratified the new agreement December 10, and Canada is expected to follow suit in coming weeks.

For Trump, the "colossal victory" of USMCA fits neatly into his "America first" campaign message ahead of a difficult November reelection fight and his current battle to see off impeachment over alleged abuse of power.

"Two decades of politicians ran for office vowing to replace NAFTA... yet when selected they never even tried," he told government members, lawmakers, union representatives and selected workers assembled at the White House's South Portico.

"I'm not like those other politicians -- I guess in many ways," he said. "I keep my promises."

Under NAFTA, "we lost our jobs, we closed our factories and other countries built our cars. But we changed that," he said. "The USMCA closed these terrible loopholes."

US Trade Representative Robert Lighthizer, who led Washington's negotiations both with USMCA and the recent truce in an even higher-stakes trade battle with China, called it a "great, historic agreement."

NAFTA, he said, had been "highly controversial from the start" and many lawmakers subsequently "came to regret" their support.