As the British colonies on the eastern seaboard grew ever more crowded in the mid-1700s, colonists began to look westward, beyond the Appalachian Mountains, and imagine the incredible riches the continent had to offer. At first, only the hardiest souls wandered far from civilization into the unknown. The stories these early adventurers told—first of the thick forests of the Ohio Valley, and later of the mineral-rich mountains in California, Colorado, and Nevada; the grassy plains of Texas and the Oklahoma and Kansas territories; and the fertile Willamette Valley of the Oregon territory—thrilled and shocked the incredulous but curious easterners.

Early wars and land purchases legalized Americans' claim to the continent (see Chapter 1). But these wars did not open the West—individuals did. Acting alone or in small groups, brave individualists ventured into virgin territory to claim what seemed to be "free...