Complex sentence: In the wake of the attack, Olson urged calm from Californians in a plea for racial tolerance, broadcasting on December 14 that he had had assurances from "every racial group" of their loyalty and devotion to the United States.
Split into simpler sentences: In the wake of the attack, Olson urged calm from Californians. In a plea for racial tolerance, he broadcasted on December 14 that he had had assurances from "every racial group" of their loyalty and devotion to the United States.