It took >100 years for them to deal with it. It was often much worse than China now.

In the UK, in the 1800's, millions moved to London, and lived in shocking slum conditions. Life expectancy was ~30 years, diseases like cholera killed many, because of overcrowding and poor sanitation. Pollution was awful, As recently as 1952, 10,000 people died in four days in the great smog of London https://en.m.wikipedia.org/wiki/Great_Smog_of_London.

In summary, it took a long time to address the problem.

Shanghai had 13 million in 2004 when I left, moved back last year and there is now 23-24 million people. I can't really name any western city that saw a population increase of 10 million in 13 years.

The US enacted descriminatory and racist immigration policies which they still have now.