Complex sentence: This followed several decades of immigration to the cities by elements considered alien by the earlier immigrants and was a result of the cultural shifts and modernizing trends of the Roaring 20s, culminating in the presidential campaign of Al Smith.
Split into simpler sentences: This followed several decades of immigration to the cities by people considered alien to earlier immigrants. It was also a result of the cultural shifts and modernizing trends of the Roaring 20s, culminating in the presidential campaign of Al Smith.