Complex sentence: This changed in the 1930s, when the rising Indonesian film industry began incorporating kroncong, and then even more so in the mid- to late 1940s, when it became associated with the struggle for independence.
Split into simpler sentences: This changed in the 1930s, when the rising Indonesian film industry began incorporating kroncong. And then even more so in the mid- to late 1940s, it became associated with the struggle for independence.