In 1940 there were 251,000 African-Americans living in Philadelphia, out of a total population of 1,931,000 or 13 percent of the population. In 1970, there were 655,000 African-Americans living in Philadelphia out of a total population of 1,948,000 or 33.6 percent of the population.  Thus, Philadelphia’s African-American population almost tripled in both numbers and as a share of the population. Much of the growth in the African-American population is explained by the “Great Migration.”
The African-American immigrants in search of better lives received a frosty welcome in the City of Brotherly Love. First, the white city had strong local ethnic identities: South Philadelphia was Italian; Pennsport, Gray’s Ferry, Kensington, Fishtown, and much of Northeast Philadelphia were Irish; Port Richmond was Polish. During the Sixties and Seventies, these people felt themselves in crisis. Many of them worked blue-collar manufacturing jobs. In 1951, 46 percent of Philadelphia workers earned a living from manufacturing. After the war, Philadelphia began to lose many of these jobs: by 1977, only 24 percent still worked in manufacturing. During the Seventies, Philadelphia lost 100,000 manufacturing jobs.
Second, the cost of government rose dramatically, from over $100 million (1947) to over $500 million (1970). Hence, from 1961 on, budget shortfalls led to repeated increases in both the real estate and wage taxes.
Third, the national murder rate went up from the late 1950s through 1974. In 1955 it stood at 4.5/100,000 people; in 1974 it stood at 10.2/100,000. This trend and other increases in violence, hit Philadelphia as hard as anywhere else. Since the Forties, “the complexion of urban crime had changed…as big cities turned blacker, so did big city homicides.”
Fourth, racism was a real force. The early post-war out-migration by whites opened up housing for African-Americans in formerly all-white neighborhoods. “Throughout the city and its suburbs, wherever blacks sought to move freely in the housing market there was community tension and frequently vandalism, intimidation, street riots, and evacuation of whole neighborhoods by whites.” For example, South Philadelphia and Kensington lost from 15 to 30 percent of their populations in the Seventies. Also, African-American migration into previously white-dominated areas changed the composition of the public schools. In 1961 there were 250,000 students in the public schools, about equally divided between whites and black. In 1970 there were 291,000 students in the system, 63 percent non-white and 37 percent white.
Philadelphia’s white population hardly formed a single block. To over-simplify, however, the blue-collar and lower middle-class “ethnics” wanted a campaign of resistance, while upper middle-class “elites” wanted change. The former had the votes. They twice elected Frank Rizzo, the tough former police commissioner, as mayor (1971, 1975). Thus, majority opinion on integration in one Democrat-governed city in the Seventies. A time of troubles.
 Timothy Lombardo, Blue-Collar Conservatism: Frank Rizzo’s Philadelphia and Populist Politics (2019).
 Nicholas Lemann, The Promised Land : The Great Black Migration and How It Changed America (1991); Isabel Wilkerson, The Warmth of Other Suns: The Epic Story of America’s Great Migration (2010).
 Russell Weigley, Philadelphia, pp. 664-665.
 Roger Lane, Murder in America, p. 303.
 Lane, Murder, p. 273.
 Weigley, Philadelphia, p. 669.