The West uses too much water. For such a simple problem, the obvious solution — use less — lies frustratingly out of reach.

That inability to change may seem hard to understand, but the root of the problem becomes clearer if we consider the role of the West in the historical development of the United States:

The purpose of our system of “free water” — heavily subsidized water for irrigation — was to provide opportunities to settlers.

The frontier has served an important function in the Euro-American imagination since before there was a United States. For historians of the American West like me, the significance of the frontier has been at the center of our field for more than a century. Thomas Jefferson made the most notable case for westward expansion, prescribing it to relieve the social and political pressures that were building up as eastern populations grew and fought over limited resources. By the mid-1800s policymakers believed his ideal of yeoman homesteaders and their patchwork of farms was the Manifest Destiny of the United States’ exceptional democracy.

But that ideal never made it all the way across the continent. It ran into a problem right around the 100th meridian, west of which there wasn’t enough rainfall for agriculture.

Agriculture would require irrigation. A lot of it.