The AFL–CIO was formed in 1955 when the American Federation of Labor and the Congress of Industrial Organizations merged after a long estrangement. Union membership in the US peaked in 1979, when the AFL–CIO's affiliated unions had nearly twenty million members. From 1955 until 2005, the AFL–CIO's member unions represented nearly all unionized workers in the United States. Several large unions split away from AFL–CIO and formed the rival Change to Win Federation in 2005, although a number of those unions have since re-affiliated, and many locals of Change to Win are either part of or work with their local central labor councils. The largest unions currently in the AFL–CIO are the American Federation of Teachers (AFT) with approximately 1.7 million members, American Federation of State, County and Municipal Employees (AFSCME), with approximately 1.4 million members, and United Food and Commercial Workers with 1.2 million members.
