The years of 1898–1945 saw New York City consolidate and come to dominate American life. New York City became the capital of national communications, trade, and finance, and of popular culture and high culture. More than a fourth of the 300 largest corporations in 1920 were headquartered there.
The era began with the formation of the consolidated city of the five boroughs in 1898, with a total population of 3.4 million. New transportation links, especially the New York City Subway, opened in 1904, bound together the new Metropolis. Increased immigration of unskilled Catholic and Jewish workers from Southern and Eastern Europe expanded the labor force until the World War ended immigration in 1914. Labor shortages during the war attracted African Americans from the Southeast, who headed north as part of the Great Migration. They sponsored the Harlem Renaissance of literature and culture celebrating the black experience.
The Roaring Twenties were years of glamour and wealth, highlighted by a construction boom, with skyscrapers dueling higher and higher in the famous skyline. New York's financial sector came to dominate the national and the world economies. The city's economy was generally prosperous after 1896, with a few short dips, until the decade-long Great Depression, which began with a Wall Street in late 1929. The economy recovered by 1940 and flourished during the World War II years. The main bases of the economy were construction, ocean shipping, garments, machine tools, and printing. Labor unions rose and fell and rose again. New York boasted the nation's strongest financial system, a large upscale market for luxury goods, and a flourishing high culture based on many philanthropists, museums, galleries, universities, artists, writers, publishers, magazines and journalists.
The Democratic political machines in the boroughs generally controlled politics. However, they were finally overthrown in 1933 by reformers who elected and repeatedly reelected Fiorello La Guardia. Heavy federal patronage helped convert the city to a stronghold of the New Deal Coalition and the model of heavy government spending on infrastructure.