Final answer:
The Europeans called the Great Plains the "great American desert" due to its perception as an arid, unproductive region, a view which began to change in the mid-1800s with the rise of Manifest Destiny.
Step-by-step explanation:
The Europeans named the Great Plains the "great American desert" because they perceived it as a useless place, unfit for civilized settlement. Major Stephen Harriman Long reinforced this perception during his exploration by frequently describing the Great Plains as an arid region, suitable only as a 'great American desert.' This view persisted until the mid-nineteenth century when attitudes began to shift due to a combination of economic opportunity and ideological encouragement, notably the concept of Manifest Destiny.
Despite being seen as useless land, the Great Plains were home to a number of Native American tribes who used the land for hunting and farming before being forcibly moved onto reservations. The European perspective was significantly influenced by their belief in private land ownership and the utilitarian value they placed on natural resources.