Good fences make good neighbours, it is said. Has the 49th parallel been a good fence? Historian Robert Bothwell, with characteristic wit and insight, explores the natures of Canada's relations over the past two hundred years with its closest naighbour.

The United States has always played a huge part in Canadian life; aside from proximity, the similarities in economic structures and political instituions reinforce the importance of the relationship. But as Bothwell points out, other forces have significantly shaped Canada-US affairs; most notable are Canadian concerns with national...