Complex sentence: Human zoos have been an important component of both "popular racism" and racialism, popularizing colonialism to the masses and was a subject of curiosity for anthropology and anthropometric studies, until at least the 1930s.
Split into simpler sentences: Human zoos have been an important component of both "popular racism" and racialism. It popularized colonialism to the masses and was a subject of curiosity for anthropology and anthropometric studies, until at least the 1930s.