Complex sentence: The Tammany Hall political machine's hold on the city, already weakened by Rothstein and the conflict over his former empire, was largely eliminated in the ensuing scandal, which also led to the resignation of New York City Mayor Jimmy Walker.
Split into simpler sentences: The Tammany Hall political machine's hold on the city was largely eliminated in the ensuing scandal, as it was already weakened by Rothstein and the conflict over his former empire. This also led to the resignation of New York City Mayor Jimmy Walker.