This one is pretty simple; for over 300 years, one family ruled Florence, Italy. They were staunchly independent and didn’t want to succumb to the papacy, so the Pope at the time, Pope Sixtus IV ordered their assassination.

The plot failed, and the family hired to do the job was banished from the city. The pope got away with the attempted murder and put religious sanctions on the city, which only strengthened the hand of the Medicis and further fragmented the city states of Italy for a century.