Complex sentence: By 1930 he had become involved with the nationalist movement, delivering speeches at the 1930 Youth Congress and teaching at Taman Siswa, a school run by native Indonesians for native Indonesians.
Split into simpler sentences: By 1930 he had become involved with the nationalist movement. He also taught at Taman Siswa, a school run by native Indonesians for native Indonesians.