Why did Rome switch governments from a representative republic to an empire ruled by a powerful leader?

Plz me in 1756 george washington was sent on a mission to, a. build a fort at the point where the allegheny and monogahela rivers form the ohio river. b. attack the french at fort duquesne. c. attack the french at fort neccessity. d. deliver a message to the french demanding that they leave the ohio valley.