Complex sentence: In 1883, Kautsky founded the monthly "Die Neue Zeit" ("The New Times") in Stuttgart, which became a weekly in 1890, and was its editor until September 1917, which gave him a steady income and allowed him to propagate Marxism.
Split into simpler sentences: In 1883, Kautsky founded the monthly "Die Neue Zeit" ("The New Times") in Stuttgart, which became a weekly in 1890. He edited the magazine until September 1917: this gave him a steady income and allowed him to propagate Marxism.