The history of the United States (1865–1918) covers Reconstruction, the Gilded Age, and the Progressive Era, and includes the rise of industrialization and the resulting surge of immigration in the United States. This period of rapid economic growth and soaring prosperity in North and West (but not the South) saw the U.S. become the world's dominant economic, industrial and agricultural power. The average annual income (after inflation) of nonfarm workers grew by 75% from 1865 to 1900, then grew another 33% by 1918.
With a decisive victory in 1865 over Southern secessionists in the Civil War, the United States became a united and powerful nation, with a more strong national government. Reconstruction brought the end of slavery and citizenship for the ex-slaves, but their political power was later rolled back and they became second class citizens under a "Jim Crow" system of segregation. Politically the nation in the Third Party System and Fourth Party System was mostly dominated by Republicans (except for two Democratic presidents). After 1900 the Progressive Era brought political and social reforms and the modernization of many areas of government and society, such as new roles for education and a higher status for women.
In an unprecedented wave of European immigration, 27.5 million new arrivals between 1865 and 1918 provided the labor base for the expansion of industry and agriculture and provided the population base for most of fast-growing urban America.
By the late nineteenth century, the United States had become a leading global industrial power, building on new technologies (such as the telegraph and steel), an expanding railroad network, and abundant natural resources such as coal, timber, oil and farmland, to usher in the Second Industrial Revolution.
There were two important wars. The US easily defeated Spain in 1898, which unexpectedly brought a small empire. Cuba quickly was given independence, and eventually also the Philippines in 1946. Puerto Rico and (and some smaller islands) became permanent possessions, as did Alaska, added by purchase in 1867, and the independent Republic of Hawaii, which voluntarily joined the U.S. in 1898.
The United States tried and failed to broker a peace settlement for World War I, then entered the war to oppose German militarism. After a slow mobilization the U.S. produced a decisive Allied victory thanks to American financial, agricultural, industrial and military strength.