Complex sentence: When 500 porters meeting in Harlem on August 25,1925 decided to make another effort to organize, they therefore not only launched their campaign in secret but also chose Randolph, an outsider beyond the reach of the Company, to lead it.
Split into simpler sentences: When 500 porters met in Harlem on August 25,1925, they decided to make another effort to organize. During this meeting, they not only launched their campaign in secret, but also chose Randolph, an outsider beyond the reach of the Company, to lead it.