"This is probably one of the most significant changes in US international economic policy in the last 50 or 60 years," an expert tells AFP shortly after US President Donald Trump unveiled a raft of punishing tariffs targeting countries around the world. "There's definitely a number of strains going on here. One is certainly a certain form of isolationism and looking inwardness," Joshua Meltzer, a senior fellow in the Global Economy and Development program at the Brookings Institution, says of the move, which targets some of the US's closest trading partners. "I think what's animating the president and tariffs at the moment has been a long-held belief that the trading system is not fair for the US," Meltzer adds. IMAGES AND SOUNDBITES