Wilderness is land that has not been modified by human activity.
For most of human history, the greater part of the Earth's terrain was wilderness, and attention was focussed on the settled areas. During the 19th century, it became clear that in many countries, wild areas had either disappeared or was in danger of disappearing, which gave rise to the conservation movement.
The creation of national parks was sufficient to preserve especially attractive or notable areas for recreation, but the support of recreation resulted in the development of untouched areas, and in the 20th century the concept of wilderness area was formally defined, and areas set aside in which human modifications are not allowed.
Even so, the areas of wilderness on Earth continue to shrink.