What caused the higher percentage of minorities in cities in the 1950s?

White flight.

Explanation:

White flight refers to the large scale migration of white families from the cities to the suburbs, especially during the 1950s-1970s. Some of the main causes of white flight were:

- The end of segregation laws meant that African Americans and other minorities could legally settle in formerly white-only neighborhoods, especially close to urban centers.

- Increased living standards meant that the generally more affluent white families could afford bigger housing in the outskirts of the cities.

- Development of road systems and phasing out of large public transportation networks meant cars became the preferred means of transport, especially for white families who could afford them. People could live relatively far away from their workplaces and commute by car.

White flight meant a radical change in the demographic composition of cities in the US. As more and more white families left, and as people of color moved to urban centers, the racial makeup of cities changed dramatically. In Detroit, white Americans comprised 83.6% of the population, while African Americans accounted for 16.2% of the total. By 1970, whites accounted for 55.5% of the Detroit residents, while African Americans were now 43.7% of the city's population.

White flight; the move of white city-dwellers to the suburbs to escape the influx of minorities.