I was watching a video of London in the year 1900. There were very few humans who hard dark skin. Well, even no humans who had dark skin.

The British Empire was the largest empire and had the largest city, which was London. Because London was a global city and the largest city, it should have had many more immigrants. Immigration to the United Kingdom from other British countries was restricted in 1962. The British Pound Sterling was before as significant as the US Dollar is today. The UK government encouraged immigration after 1945 because of World War 2.

This is what I do not understand. Why was there not mass migration to London before 1945? And why was migration to London was still little but larger between 1945 and 1962? I think that London seemed very attractive to the humans of British India because the UK was much more developed than British India was. I think that the indigenous peoples of South Africa and Australia were treated badly, so they should have escaped to the UK. The most shocking thing is that the UK did not have visa restrictions until 1962, so it is not as if there were restrictions about immigrating from a poor British undeveloped country like the British Raj to a very developed country with the international currency like the United Kingdom.

My question is this.

Why was there little immigration to London before 1945? And why was there still little immigration before 1962, despite that the British Empire and a population of greater than 100,000,000. I would have expected that immigrants would arrive in millions per year to the United Kingdom from developing countries.

Also, I do not need sources, because I only care about the answers and I do not check the sources and I do not want you to waste your time with finding the sources and confirming the sources.