Washington, April 30 -- Britain's King Charles III urged the United States on Tuesday to stand firm with its Western allies, as strains over Iran and Ukraine risk undermining transatlantic ties facing their most serious test in years. "The challenges we face are too great for any one nation to bear alone," he said in a speech at the US Congress, calling for partners to defend shared values. "Whatever our differences, whatever disagreements we may have, we stand united in our commitment to uphold democracy," the monarch told lawmakers. Addressing Congress during celebrations marking 250 years since American independence from Britain, Charles stressed the historic ties between the two nations, saying their partnership was "born out of dispute...