Early groups of Scandinavian immigrants to the United States had been motivated by religious factors, namely small communities of religious minorities who left to break from Lutheran state churches. Although small numbers of Scandinavian immigrants had already established themselves in the United States, the largest number immigrated during the 19th century in response to population increases across Scandinavia. During the 19th century, the population of Denmark, Norway, and Sweden collectively tripled. This increase was likely caused by improved medical and agricultural practices, and the unusually peaceful era in the region which followed the Napoleonic Wars. As a result, mortality rates dropped, while the birth rate continued to be high. The region's existing infrastructure could not support such extreme growth. In particular, population growth strained the resources of rural populations, where usable land was already limited. With more children to support, farms were successively split into smaller plots to be divided among descendants, and families were increasingly unable to sustain themselves from their own land. This forced many people in rural communities into poverty. Some chose to migrate to urban areas, in turn increasing unemployment. A later recession during the 1860s and famine further drove Scandinavians to emigrate. Although immigration to the United States decreased during the American Civil War, a significant wave again left during the 1880s. By the 1920s, the number of Scandinavian immigrants had decreased greatly, stopping almost entirely during the Great Depression.
Between 1825 and 1930, approximately three million Scandinavians emigrated, over 95 percent of which moved to the United States. It is estimated that this group comprised 1.2 million Swedes, 850,000 Norwegians, and 300,000 Danes. Initially, it was common for families to relocate as a whole unit and settle in the rural areas, most often in the Midwest. This shifted by the late 1800s, which saw more unmarried individuals immigrate to urban areas. They were often followed by other members of their family once they had financially established themselves. Similarly through chain migration, immigrants often settled near those they already knew from their country of origin. This led to distinct communities of Danes, Swedes, and Norwegians that expressed regional differences.
While some immigrants quickly assimilated, many of the resulting insular rural communities remained culturally distinct. They established their own churches, newspapers, and schools in their native language and in accordance to their traditions. Institutions like these helped preserve their cultural identity, though over time these communities began to assimilate. Their identity came to be more homogeneously Scandinavian, rather than defined exclusively by their ancestral country. This paralleled global conceptions of Scandinavism, as different nationalities were led to work together by proximity.
Following World War II, there was an increase in interest in ethnic origins in the United States, which saw more Scandinavian Americans refer to themselves as Norwegian-American, Danish-American, etc. Remaining communities became concerned with cultural activism and preservationism. These efforts often centered around church congregations and societies, such as the Sons of Norway and the Swedish–American Historical Society. Although use of Scandinavian languages has largely died out among descendants of the 19th century, Scandinavian identity has been maintained, especially in rural communities
