Complex sentence: Rostow claimed that these stages of growth were designed to tackle a number of issues, some of which he identified himself; and wrote, Under what impulses did traditional, agricultural societies begin the process of their modernization ?
Split into simpler sentences: Rostow claimed that these stages of growth were designed to tackle a number of issues. Some of which he identified himself and wrote, Under what impulses did traditional, agricultural societies begin the process of their modernization?