Complex sentence: In order to increase his power as a political boss, Platt in 1898 steered passage of the Greater New York bill, which incorporated the boroughs of Brooklyn, Queens, and Staten Island into the city and created New York City as it exists today.
Split into simpler sentences: In order to increase his power as a political boss, Platt steered passage of the Greater New York bill in 1898. The bill incorporated the boroughs of Brooklyn, Queens, and Staten Island into the city, thereby creating New York City as it exists today.