By the late 1880's New York was the commercial capital of the country.  It feared that it would be overtaken by Chicago's rapidly increasing population.  There was an issue about water supplies; wells near Brooklyn were turning brackish and which even brought down Mayor Chapin in 1892 but New York had built the Croton Aqueduct.  With the completion of the Brooklyn Bridge, it was easy for people to live in Brooklyn and work in New York so many did.  The idea of consolidation of the two cities was proposed multiple times and voted down.  It was very contentious with people squabling about taxes.  On May 4, 1896 it finally passed and Governor Frank Black signed it into law.  The new city would consist of Brooklyn, New York, part of Queens County, Richmond, and what eventually became the Bronx.  It's 3,000,000 people would make it the largest city in the US and the second largest in the world after London.