text: It was approved by the federal government in 1911. The annexation was controversial at the time, as an overwhelming majority of Allegheny City residents were opposed to the merger. Previous Pennsylvania law had directed that a majority of the voters in each merging municipality had to approve an annexation agreement. In 1906, the State Assembly passed a new law that authorized annexations if a majority of the total voters in both combined municipalities approved the merger. The annexation was rejected by the residents of Allegheny City by a 2:1 margin, but was approved by much more populous Pittsburgh residents, and the annexation bill passed into law. Allegheny City residents tried unsuccessfully for years to have the annexation overturned in court.
  The population of Pittsburgh rose from 321,616 in 1900 to 533,905 in 1910, which included the 132,283 who lived in Allegheny in 1910, when the last separate census of Allegheny was taken.
  When the two cities were joined, both of the old ward systems were discarded. A new ward system was established made up of 27 wards. In the new ward system, Allegheny was divided into wards 21 to 27. Its past territory is easily seen by viewing a map of the city wards.
  In the 1960s, Pittsburgh undertook a massive urban redevelopment project that demolished the historic core of Allegheny City, leaving only the Commons of Allegheny Center and its surrounding neighborhoods. The Carnegie Library, the Old Post Office Building, and the Buhl Planetarium buildings were not demolished.  Major portions of the neighborhoods of Allegheny West, Manchester, Central Northside, California-Kirkbride (Old Allegheny Rows), and East Allegheny are listed on the National Register of Historic Places, including the Mexican War Streets in Central Northside.