Demography and War. Rapidly growing populations are often aggressive. They both enjoy and suffer from an abundance of young men seeking new places for themselves in the world because a plurality of sons cannot all inherit a father's property without suffering an unacceptable decline of living standards. As long as the majority of Americans lived on farms and had lots of children, this circumstance fueled rapid frontier expansion at the expense of Indian peoples. Easy victories in sporadic warfare were essential to the expansion of American settlement, beginning in the 1630s and lasting until 1890, when the final armed clash between the U.S. Army and an Indian people took place at the Battle of Wounded Knee, South Dakota (1895). American military successes in turn reflected an abundance of armed men—militiamen in colonial times supplemented after independence by professional soldiers—who were willing and ready to invade Indian territory and seize new lands from the occupants.

Nonetheless, the demographic disasters that crippled the Indian population of North America were not primarily due to warfare. Indian communities were disrupted instead by repeated exposures to lethal diseases imported from the Old World, to which they initially had no inherited resistance. The result was a vicious circle: epidemic disease deaths weakened, when they did not paralyze, armed resistance; and sporadic defeats in war deprived survivors of any chance of recovery.

The upshot was a drastic repeopling of the broad swathe of the North American continent that frontier expansion brought within the boundaries of the United States. Starting from two tiny shoreline footholds in 1607 and 1620, English colonists quickly achieved rapid rates of population growth that carried the frontier across the Appalachians in the late eighteenth century, and across the Rockies some sixty years later. Africans, who crossed the ocean as slaves, and immigrants from Europe, who came initially as indentured servants, added additional strands to the repeopling of the country.

Throughout the colonial period, local militias conducted sporadic local offensives against Indians with only occasional regard for British imperial policy. But when imperial wars broke out in the Americas, colonial militamen played a significant support role, and on several occasions (1710, capture of Port Royal; 1745, capture of Louisburg) carried through successful offensive operations. French and Spanish colonists in America were too few to support their home governments with comparably numerous or well‐organized military units. This was a factor—though scarcely the primary factor—in British successes in the decisive French and Indian War of 1754–63 that added Canada and Florida to Great Britain's American empire.

But, almost at once, their remarkable demographic expansion allowed the colonists to leave their European rivals behind and (with help from France) to break their political bond with Great Britain in the Revolutionary War. Former imperial restraints on frontier expansion and military aggression against the Indians were removed after the United States became sovereign. As a result, rapid population growth together with improvements in transport raised the westward movement to flood proportions during the first half of the nineteenth century. Local militiamen continued to play the principal role in Indian fighting and frontier expansion until the Mexican War (1846–48), when regulars of the U.S. Army fought their way to Mexico City and compelled the Mexicans to cede California and the rest of their northern territories to the victors.

The Civil War was by far the most costly conflict ever fought by Americans. The North enjoyed a definite demographic advantage from the start, with a total population of about 21 million opposing about 9 million Southerners, of whom 3.5 million were black slaves. More than 1.5 million soldiers served in the Union army, and suffered an official total of 359,528 deaths from lethal infections and battlefield casualties. The Confederates enrolled some 800,000 soldiers, and suffered about 258,000 deaths, so that the combined loss of life from the war exceeded 600,000. Such a trauma slowed but did not stop population growth for the nation as a whole, but aftereffects kept the South depressed and backward for the following two generations. The North suffered proportionately less, and an increasing flow of European immigrants more than made up for wartime losses.

A fundamental change in American demography and warfare set in between 1870 and 1890 when land suitable for pioneer cultivation disappeared after the frontier of settlement encountered the dry landscapes of the high plains. As a result, by about 1890, when the U.S. Census report announced that the open frontier had disappeared, the demographic regime that had sustained white territorial expansion at Indian expense for the preceding 270 years broke down. Instead of seeking new land to cultivate, surplus children from rural families headed into town, where industrial manufacturing and service jobs presented them with a radically different style of life—whether they arrived from American farms or from European villages across the ocean. Consequently, in 1920 the U.S. Census recorded an urban majority for the first time, and in en suing decades the American countryside emptied out so that fewer than 5 percent of the population are today employed as farmers.

Wars fought by the United States since 1898 both reflected and affected these demographic and social changes. Superficially, the Spanish‐American War (1898) looked like the translation of old‐fashioned frontier war to Cuban soil; but the aggressive dynamic of American rural society was already slackening. As a result, after the familiar sort of easy victory, the United States refrained from annexing Cuba, and despite an uneasy conscience, settled for annexing Puerto Rico and the Philippines. Overseas islands, already occupied by farming populations, were not available for frontier settlement in the old way, and the drive for territorial expansion was therefore far weaker than before.

World Wars I and II were far more serious engagements, and provoked more thorough mobilization of the entire nation than had been possible during the Civil War, when a majority of the population had to remain working in the fields in traditional ways to assure sufficient food. About 4 million men were recruited undrafted into the army during World War I and a total of 1.2 million crossed the ocean to France. But these figures were dwarfed during World War II, when about 15 million men and women served in many different theaters of war and remained in uniform for a longer time than had been necessary in 1917–18. Yet military deaths in both wars totaled less than 410,000, almost a third fewer than in the Civil War—a tribute, more than anything else, to advances in military medicine that had taken place since 1890.

Wartime experience for so many millions in 1917–19 and again in 1941–45 had dramatic demographic impacts. Postwar baby booms were in both cases succeeded by an accelerated decline in birth rates, so that by 1990, births in the United States was just about at the replacement level—2.1 children per woman of childbearing age. Total population continued to grow rapidly, thanks to the relaxation of legal barriers to immigration after World War II; but without the inflow of newcomers, the population of the United States would no longer replace itself.

Many factors contributed to this radical departure from the earlier pattern of American demographic expansion—urbanization chief among them. But informal exposure to a long‐standing professional military tradition of sexual habits designed to prevent unwanted births, supplemented by official medical efforts at inhibiting the spread of venereal disease, affected the behavior of millions of conscripted soldiers. This wartime experience surely (but secretly) carried over into civilian life, altering sexual habits and expectations much more rapidly than could otherwise have occurred. Birth rates plummeted to less than half of what they had been in the colonial era.

A second aspect of wartime mobilization, 1917–19 and 1941–45, confirmed and extended this basic demographic shift. Wartime labor shortages allowed and invited millions of women to start working outside the home; and not all of them resumed a merely domestic style of life when peace returned. By the 1960s, earning their own money by working for wages became a badge of women's liberation, and the costs of childbearing and infant nurture became correspondingly harder to bear. This kept birth rates low, opening the United States to newcomers from crowded rural communities in Latin America and elsewhere.

The repeopling of America, begun so radically in 1607, thus assumed a new guise in the 1960s. Except for an influx of Vietnamese refugees after the U.S. forces left the Vietnam war in 1973, warfare has had little significance, at least so far, for this second chapter in the exceptional demographic instability that distinguished the British North American colonies and the United States of America throughout their history.
[See also Casualties; Mobilization; Society and War.]

Bibliography

Richard E. Easterlin , Population Change and Farm Settlement in the Northern United States, Journal of Economic History, 36 (1976), pp. 45–75.
Rudy Ray Seward , The American Family: A Demographic History, 1978.
Lawrence Delbert Cress , Citizens in Arms: The Army and Militia in American Society to the War of 1812, 1982.
John E. Ferling , A Wilderness of Misery: War and Warriors in Early America, 1980.
Robert M. Utley , The Indian Frontier of the American West, 1846–1890, 1982.
William H. Chafe , The Paradox of Change: American Women in the Twentieth Century, 1991.

William H. McNeill