How the West Was One

There is no epigraph in Tim Cook’s authoritative history of Canadian-American cooperation during the Second World War, though the prolific historian at the Canadian War Museum could have plucked the final words of Shakespeare’s Sonnet 30: “But if the while I think on thee, dear friend, / All losses are restor’d, and sorrows end.” For when North Americans “summon up remembrance of things past”— the sonnet’s second line — their happiest memories may include the work that William Lyon Mackenzie King, Franklin Delano Roosevelt, and millions of unsung soldiers, sailors, aviators, makers of matériel, and others performed before and during the conflict.

Two countries, both alike in dignity, where civil blood made civil hands clean.

They conferred, mostly without conflict. They came together to strategize, often to great effect. They fought alongside each other, at times with astonishing force. They teamed up in Alaska, to ship planes to the Soviet Union...