Pre-emption

Pre-emption, right of individuals to purchase land or goods before others and the act of such purchases. During the 1800s more than 200 million acres (81 million hectares) of government-owned land in the United States passed into private hands through pre-emption. Squatters settled lands they didn't own and usually built homes there. The federal government passed laws allowing them to purchase the land cheaply before it was offered for sale to anyone else. The practice was abolished in 1891.