Before order was finally restored, angry mobs had destroyed or damaged more than 350 buildings, including the residence of the Home Minister and 70 percent of the police boxes in the city. Casualties included 17 people killed, over 450 policemen, 48 firemen and civilians injured, and hundreds arrested. News of the Tokyo violence touched off similar disturbances in Kobe and Yokohama and further stimulated hundreds of nonviolent rallies, speeches, and meetings throughout Japan for the next several months. This unrest directly contributed to the collapse of Prime Minister Katsura Tarō's cabinet on 7 January 1906. The Hibiya Incendiary Incident marks the beginning of a period in Japanese history that historians call the Era of Popular Violence . Over the next 13 years Japan would be rocked by a series of violent protests , culminating in the Rice riots of 1918.
Question: How many other cities were set off by the events taking place in Tokyo?
Answer: 2