You have to be careful while studying Gustave Le Bon and his works. He was a product of his times and so there is an undercurrent of racism in this book due his being influenced by pseudo-scientific "Social Darwinism" theories - https://en.wikipedia.org/wiki/Social_Darwinism
Approach it as just a sociological/psychological case study of the 1800s and there is much to learn.
The guy was horrified by Napoleon and the violence of the French Revolution, so he mainly spends the book criticizing his fellow white catholic people in France. Yes, he says racist things about other nations, but the parts about France which was all his exact same ethnic group / religion are more timeless.