Final answer:
The St. Valentine's Day massacre in Chicago most likely spurred authorities into action due to the enormous amount of violence connected to this event.
Step-by-step explanation:
The St. Valentine's Day massacre in Chicago most likely spurred authorities into action due to the enormous amount of violence connected to this event. The massacre involved the brutal killing of seven members of a rival gang by Al Capone's gang, and it shocked the public with its brutality and bloodshed. The FBI increased resources to get at the mob bosses in Chicago and shut down their organizations as a response to this high-profile and shocking event.