In a fascinating history of the Chamizal dispute, Paul Kramer considers what happens when nature refuses to respect national boundaries:

The whole point of setting the border between Mexico and the United States at the deepest channel of the Rio Grande was that the river was not supposed to move.

That was the thinking in 1848, when, following Mexico’s defeat by the United States and surrender of its vast northern lands, boundary surveyors from the two countries were tasked with reinventing the border. The choice of the river for the boundary’s eastern half had been obvious: its use as a territorial marker stretched back into the region’s Spanish colonial past, and it was hard to miss and often difficult to cross. But even as he filed his report on the completed boundary survey, in 1856, Major William Emory cautioned that the river might be an unreliable partner in border making…