1845 Texas, formerly part of Mexico, is incorporated into the United States.
1846 Britain signs Oregon over to the United States.
1848 New Mexico and California are annexed after the Mexican–American War.
1861 The first transcontinental telegraph line is completed; the Pony Express mail service closes two days later.
1862 The Homestead Act grants 160 acres of free land to anyone settling it.
1869 The first transcontinental railroad is completed.
1890 The US Census Bureau closes the American frontier, since no more large areas of land are unsettled.
The belief by sometime journalist John L. O’Sullivan that the ...