US-Canada trade talks have collapsed after Canadian Prime Minister Mark Carney rejected Washington’s proposed terms as “unfair” and “uneconomic.” Carney accused US President Donald Trump of launching a trade war against Canada and vowed to protect Canadian economic interests. New 50% US tariffs on around $20 billion worth of Canadian goods have come into force, with Ottawa promising dollar-for-dollar retaliation from September 8. The escalating dispute threatens jobs, businesses and long-standing cross-border economic ties between the two North American neighbours.