Complex sentence: When word of Lincoln's assassination reached San Francisco, angry citizens stormed the offices of the newspaper that would become "The Examiner," wrecked it and set fire to it, as the "Daily Democratic Press" had been a pro-Confederacy, pro-slavery newspaper.
Split into simpler sentences: When word of Lincoln's assassination reached San Francisco, angry citizens stormed the offices of the newspaper that would become "The Examiner," wrecked it and set fire to it. The "Daily Democratic Press" had been a pro-Confederacy, pro-slavery newspaper.