President Abraham Lincoln enacted the Homestead Act of 1862, one year after the dawning of the Civil War, just after 11 states had already seceded from the union. One purpose of the act was to stimulate settlement and development of the western half of the United States, but the act also tied those western settlers to the North of the United States, "politically and economically," which helped Lincoln strengthen the numbers of defenders of the union during the Civil War (Library of Congress, "Prairie Settlement: Nebraska Photographs and Family Letters, 1862-1912").
Lincoln's Homestead Act of 1862 granted 160 acres of U.S.-owned land to settlers provided that they built a home and grew crops, improving the land for five years. After five years, the homesteader could file for the title for free; if the homesteader wanted the the title to the land sooner, the homesteader could apply for the title in as soon as 6 months so long as the homesteader paid $1.25 per acre (National Archives, "Teaching with Documents: The Homestead Act of 1862").
The act granted land to both U.S. citizens and immigrants alike who "[have] never borne arms against the U.S. Government" (National Archives). Hence, so long as either U.S. citizens or immigrants applying for land had never fought against the U.S., they could receive their 160 acres. The only contention for immigrants was that they needed to intend to become citizens.
U.S. citizenship was defined first in the Naturalization Act of 1790, seven years after the American Revolution, and then once again in the Naturalization Act of 1795. According to the final act, U.S. a natural-born citizen is defined as any child born to U.S. citizens, even outside of the United States. The final act also defined the naturalization process for immigrants to become citizens. Immigrants can become naturalized citizens by residing in the U.S. for five years and by fulfilling the two-step process of filing a Declaration of Intention to become a U.S. citizen or other papers and being sworn in as a citizen to confirm status.