[3] The Capital city of Budapest was established on 17 November 1873 with the unification of three separate towns, named Buda, Óbuda and Pest.

In the 18th and 19th century Pest became the natural commercial, transportation, industrial and cultural center of Hungary, Buda and Óbuda remained small towns.

Between the unification and the World War I Greater Budapest quadrupled its population, got a new global city upon the Danube.

At that time Budapest was one of the fastest-growing cities in Europe, triggered by industrialisation and high natural growth rate and fertility of rural ethnic Hungarians.

Internal migration peaked in the 1960s with near 250,000 people in correlate to post World War II baby boom and forced collectivization.

This restriction raised a strong wave of suburbanization, which peaked after fall of the Communism, the number of inhabitants dropped to 1.7 million, while garden housing development is still decisive in the suburbs.

Hungarian villages and market towns become overcrowded, Budapest has become the main destination of the rural surplus population due to industrialisation.

According to the 2011 census the total population of Budapest was 1,729,040, of whom there were 1,397,851 (80.8%) Hungarians, 19,530 (1.1%) Romani, 18,278 (1.0%) Germans, 6,189 (0.4%) Romanians, 4,692 (0.3%) Chinese and 2,581 (0.1%) Slovaks.

Hungarian Calvinists increased their number from 13,008 (4.8%) to 224,169 (12.6%) between 1870 and 2001 due to internal migration, triggered by higher fertility than other denominations.

Judaism also was a significant religion in Budapest, numbered 215,512 people (23.2%) in 1920, but they dropped to a smaller group (80,000 people, 4.2% in 2018) due to the Holocaust, secularization, and atheism, the huge ratio to convert to Christianity, and assimilation and intermarriages with non-Jews after 1945, and the immigration to Israel.

Ethnic Hungarians made up the majority of non-Hungarian citizens also, primary from Romania, former Yugoslavia and Ukraine.