Since 1846, the United States has never been at war with one of its neighbors (we had a few military excursions into Mexico over the years, but they were more to keep peace at the borders and weren’t wars). This peace among huge geographically contiguous countries (the border with Canada alone is over 5,500 miles) is unknown in world history. Until the last fifty years, European borders have shifted constantly, mostly through war or the threat of war. This peace in North America and in the post-WWII period in Europe is largely possible because of the overwhelming military and economic strength of the United States. The peace is a modern version of Pax Romana, the peace that the Roman Empire imposed on its world