Complex sentence: By 1849, partly as a side effect of the California Gold Rush and the settlement of California, mail to and from San Francisco had increased greatly, and in response the Hawaiian government established a post office and set postal rates.
Split into simpler sentences: By 1849, partly as a side effect of the California Gold Rush and the settlement of California, mail to and from San Francisco had increased greatly. In response, the Hawaiian government established a post office and set postal rates.