1820s: There are fewer than 10 million people living in more than 1.7 million square miles of the United States. This averages to fewer than six people for every square mile.

1990s: The U.S. population is about 250 million on just over 3.6 million square miles of land. This averages to about 70 people for every square mile.

1820s: The United States is comprised of land stretching from the Atlantic Ocean to the Rocky Mountains. The land making up present-day Oregon and Washington is claimed by both Britain and the United States, while most of the West and Southwest is Spanish territory.

1990s: In addition to the 50 states, the United States holds the territories of Puerto Rico, the Northern Mariana Islands, American Samoa, Guam, the Federated States of Micronesia, the Republic of Palau, the U.S. Virgin Islands, as well as some smaller Pacific islands.

1830s: John Deere...