In the long and contested history of trade between nations, the United States has once again raised its walls — this time against Australia, a close ally, imposing a 12.5 per cent tariff on most Australian exports under the banner of forced labour enforcement. The move, which took effect Friday, builds on a legal framework deliberately chosen to survive the court challenges that felled earlier tariff attempts, suggesting the stated rationale may be less about supply chain ethics than about finding durable ground for economic leverage. Australia, which already runs a trade deficit with America