Albany lawmakers created the Metropolitan Police force in 1857, which had jurisdiction over both Manhattan and Brooklyn (and led to a series of riots when there were two police forces in the city, but that's another story). A joint fire department and board of health was also established later that year. In 1868 Andrew Haswell Green proposed the creation of a greater city of New York, including Brooklyn and parts of the Bronx, Queens and Staten Island, to be headed by a single mayor. This plan was stymied by Boss Tweed, although he gave the Department of Parks the authority to lay out streets from Morrisania to the Bronx River in anticipation of development. Other politicians such as Lewis G. Morris pushed for the annexation of parts of the Bronx. On January 1st, 1874, Morrisania, West Farms and Kingsbridge were incorporated into New York City, adding 7,000 acres and 40,000 people. In 1895, Manhattan annexed Wakefield, Pelham and Eastchester.

The construction of bridges across the East and Harlem rivers helped open up the Bronx and Brooklyn to residential and commercial development; the construction of the Brooklyn Bridge was facilitated by a bitter winter in 1866-67, when the East River froze over, halting ferry service. Several bridges to the Bronx were built in the 1880s and 90s, and the Navy Corps of Engineers started a series of projects meant to improve navigation between Manhattan and the industrial ports of the Bronx, dynamiting the treacherous rocks of Hell's Gate and building the Harlem River Ship Canal. Brooklyn politicians saw the success of the annexed district's ports and began to call for consolidation, as it would benefit Brooklyn's ports. The Manhattan Chamber of Commerce also called for consolidation, as they recognized that not only would the harbor of the city become so much bigger, but that more improvements could be made without divided political interests.

It was becoming evident to more politicians, planners and leaders that the creation of a Greater New York would be incredibly economically beneficial. An additional reason for consolidation came in 1889, when Chicago annexed 133 miles, surpassing Philadelphia to become the second largest city in the country; New York politicians were concerned that financial institutions and investors would leave New York for Chicago. In 1890, Andrew Haswell Green convinced the state legislature to establish a Greater New York Commission. With Green as its president, the commission concluded that the interests of all the boroughs were tied together, and that the creation of a Greater New York would wisely anticipate population growth and provide significant forethought and planning.

The greatest opposition to the consolidation plan came from a steadfast group of Protestants from Brooklyn Heights, who argued that the plan would destroy Brooklyn's identity as the city of "homes and churches" (much of their rhetoric was tinged with racism and anti-immigrant sentiments). Of course, these folks were tenaciously clinging to the past. The Brooklyn waterfront had rapidly industrialized after the construction of the Brooklyn Bridge, and major thoroughfares were established as centers of commerce and entertainment.

In 1894, in anticipation of the impending consolidation, Brooklyn consolidated the original six Dutch towns (Bushwick, Flatlands, Flatbush, Gravesend, New Utrecht). Later that year, voters went to the polls to vote on a referendum for consolidation; in every borough it passed by a large majority, except in Brooklyn, where it passed by only 277 votes. In 1896, it was signed by Governor Levi Morton, who then organized a council to oversee the consolidation and write the Greater New York charter; immediately the council gave control of the street railways to the municipal government, established borough governments and a board of aldermen and called for a uniform building code (this would lead to the New Law Tenement Act in 1901). At the stroke of midnight on January 1st, 1898, the city's population jumped to well over three million, stretching over more than 300 square miles and creating the modern city of New York, poised for greatness on the cusp of the 20th Century.