Last updated: 2018
This image shows the percentage of White people in big cities in (formerly) White countries. For the purpose of this post, "White" is defined as people of European origin, which is stricter than the US definition which includes, for example, Middle Eastern countries as "White".
It is evident that Whites have already become or will become minorities in their own countries, due to a combination of low birthrates and mass immigration. A look at the demographics of children makes this more obvious, as White people are typically over-represented among the elderly. Eastern European countries tend to be the "Whitest", probably because these countries are both poorer (less attractive to immigrants) and more nationalistic (less open to immigration) following 40 years of Soviet/communist dictatorship.
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Please note that some countries (e.g. US, UK, South Africa) have racial/ethnic census data, while most countries don't and some (France) even forbid collecting such data. These numbers are all just estimates, which is also why I decided not to put the percentage labels into the graph.
Please also note that for the US, I used the number of non-Hispanic whites. This is roughly comparable with "people of European descent", however it excludes Hispanic whites and includes the Middle East and North Africa. If Hispanics are included, some cities such as Miami or Los Angeles would have higher percentages of 'European-Americans'.
All the cities included in the image were founded by Europeans/whites and have had a European/white majority. Even in Constantinople (which was conquered by the Turks in 1453 and renamed to Istanbul in 1930), a third of the population was still Greek until they got genocided by the Turks in 1919-23.