Which two countries share the longest international border in the world?
And the answer: Canada and the United States.
At 8,893 kilometers, the land border between Canada and the United States is the longest in the world. Canada borders Alaska in the west, and 12 states of the continental U.S. in the south. The boundary is designated by a continuous 20-foot-wide treeless border known as "The Slash," with maintenance every six years.
Every year, U.S. taxpayers pay around half a cent to the International Boundary Commission (IBC) for the sole purpose of deforesting every inch of the U.S.–Canada border. Rather than a fence, wall, or any sort of physical border, the grand majority of this several-thousand mile border is a simple tree gap, stretching as far as the eye can see. The Slash, as it's called, was constructed with the sole purpose of alerting the general person of the presence of an international border.
The U.S.-Canada border was established in 1846 with the signing of the Oregon Treaty. The treaty established the 49th parallel from the Rocky Mountains to the Strait of Georgia as the boundary between the United States and British Canada. Markers were placed along the line, however, as due to a lack of GPS, border markers were inadvertently placed in a zig-zag fashion, straying north or south of the official 49th parallel border by an average of 295 feet.
Tourists and ambitious backpackers can visit the line at a number of locations. Waterton-Glacier International Peace Park on the Pacific Crest Trail, the Continental Divide Trail to Canada, or the Long Trail in Vermont will take any and all willing hikers to the infamous Slash.