access to modern healthcare across the country, ranking 26th worldwide for healthcare system quality. The construction of new hospitals and primary healthcare centers across the Kingdom, as well as healthcare during pregnancy and increased use of vaccinations account for a decline in infant mortality and increased life expectancy. UN estimates The Population Department of the United Nations prepared the following estimates. Population estimates account for under numeration in population censuses. Nationality and ethnicity Nationality noun: Saudi(s) adjective: Saudi or Saudi Arabian Ethnicity The ethnic composition of Saudi citizens is 90% Arab and 10% Afro-Asian. However, 38.3% of inhabitants (about 13.3 million people) are non-citizens, most of them are migrant workers. Urbanization The following data has been retrieved from the CIA World Factbook urban population: 83.8% of total population (2018) rate of urbanization: 2.17% annual rate of change (2015-20 est.) Historically, some of the population of Saudi Arabia followed a nomadic lifestyle, while most lived in villages and small towns ran by emirs. Following the discovery of oil in the 1930s, the Kingdom became far more settled as people moved to centers of high economic activity. Significant population growth can be seen in the rise of urbanization throughout Saudi Arabia, which has grown 2 percent in the past ten years. The largest Saudi cities have become flooded with new residents as more people move to urban cities to find better employment opportunities, and overcrowding has become a major issue across the nation. Migration Migration is a significant part of Saudi Arabia's tradition and culture, as the nation's thriving oil economy attracts large numbers of foreign workers from an assortment of countries throughout Asia and the Arab world. Following economic diversification in response to the oil boom of the 1970s, the Saudi government encouraged skilled and semi-skilled workers to enter the Kingdom as the demand for infrastructure and development intensified. Saudi Arabia is among the top five immigrant destination countries around the world, currently hosting 5.3 million international migrants in its borders. In 2017, non-native residents accounted for 37% of the Kingdom's total population, more than twice that of the United States whose immigrants make up 15% of the nation's total population. The majority of Saudi Arabia's foreign born population are males between the ages of 25 and 45. These immigrants make up a larger percentage of the total population in this age group compared to native-born Saudis ages 25–45, according to