The period began with the inauguration of Fernando Wood in 1855 as the first mayor from Tammany Hall. He was a part of a political party supported by Irish immigrants who dominated the city throughout this period. During this century, the city was transformed by immigration, a visionary development proposal called the Commissioners' Plan of 1811, which expanded the city street grid to encompass all of Manhattan. It also opened the Erie Canal, which connected the Atlantic port to the vast agricultural markets of the Midwestern United States and Canada in 1819. New York City became the largest city in the United States before 1835, after surpassing Philadelphia. Tammany Hall, a Democratic Party political machine, dominated local politics. Central Park was created from a design competition in 1857 and it became the first landscape park in an American city.

The American Civil War occurred from 1861 to 1865. New York City had both strong commercial ties to the South, and a growing immigrant population. Thus they were divided between the Union and Confederacy, which caused the Draft Riots of 1863. When the Civil War ended, the rate of immigration from Europe grew, and New York became the first place millions of immigrants sought for a new and better life in the United States. The Statue of Liberty symbolized this era when it was created in 1886.