In this photo taken Friday, December 9, 2016, young ballerinas practice under the instruction of Kenyan ballet dancer Joel Kioko, 16, in a room at a school in the Kibera slum of Nairobi, Kenya. (Photo by Ben Curtis/AP Photo)

In this Monday, June 20, 2016 photo, a Palestinian girl plays in a barrel as her mother bakes bread for a Ramadan dinner at their house in el-Zohor slum, on the outskirts of Khan Younis refugee camp, southern Gaza Strip. (Photo by Khalil Hamra/AP Photo)

Brick-carving featuring Tang Dynasty (AD 618-907) maids performing musical instruments is seen at the Chinese Music History Museum in Xian University of Architecture and Technology on September 27, 2008 in Xian of Shaanxi Province, China. (Photo by China Photos/Getty Images)

Women cry as they look for reusable household materials after fire broke at slums in Kadivali area of Mumbai, India, Monday, December 7, 2015. Hundreds of homes were reportedly destroyed as fire tenders labored to reach the source in the heavily congested area. (Photo by Rajanish Kakade/AP Photo)

A bride from the Santa Marta slum takes a break after getting her makeup done before a group wedding in Rio de Janeiro December 17, 2014. A total of 16 couples took part in a mass wedding ceremony organized by the Police Peacekeeping Unit (UPP) as part of activities geared towards social enhancement of the slums. (Photo by Pilar Olivares/Reuters)

In this July 11, 2016 photo, a young, masked drug trafficker poses for photos holding his guns at a slum in Rio de Janeiro, Brazil. Teenagers openly tote guns while they work as guards, lookouts and distributors for drug lords operating just a few miles from where hundreds of thousands and tourists and athletes will be for the Aug. 5-21 Olympic Games. (Photo by Felipe Dana/AP Photo)

A military police officer patrols in the Roquette Pinto shantytown, part of the Mare slum complex in Rio de Janeiro, Brazil, Wednesday, April 1, 2015. The Brazilian army has begun to pull out of one of Rio de Janeiro's most violent slums, with police assuming responsibility for security in the area. (Photo by Felipe Dana/AP Photo)

Two boys in the Gorbals area of Glasgow, UK on January 31, 1948. The Gorbals tenements were built quickly and cheaply in the 1840s, providing housing for Glasgow's burgeoning population of industrial workers. Conditions were appalling; overcrowding was standard and sewage and water facilities inadequate. The tenements housed about 40,000 people with up to eight family members sharing a single room, 30 residents sharing a toilet and 40 sharing a tap. By the time this photograph was taken 850 tenements had been demolished since 1920. Redevelopment of the area began in the late 1950s and the tenements were replaced with a modern tower block complex in the sixties. (Photo by Bert Hardy/Getty Images)