An Olive branch is a symbol of peace recognized worldwide.
In Ancient Greece, the olive branch was a symbol of bounty and victory. Its association with plenty comes from the essential character of the olive to the Greek economy - without it, Greek life would have been utterly lessened, and dramatically different. The branch was also awarded to Olympic victors.
In Ancient Rome, it was one of many plans with symbolic significance. As the acanthus plan symbolized order, and the oak branch victory, the olive branch symbolized peace.
The term "olive branch" is also associated with American history, specifically a final attempt by the Second Continental Congress to avoid outright warfare with Britain. After Lexington and Concord in April of 1775, the Congress had divided into two camps - a first camp, led by John Dickinson, favored avoiding war at all costs; a second minority camp, led by John Adams, believed that at this point, war was inevitable. Eventually, it was decided to send a final petition to the King. Thomas Jefferson was originally drafted to write it, but the final version was actually written by Dickinson. The petition expressed the colonists' desire not to become independent, but expressed their displeasure with the colonial governors and argued for a re-negotiation in trading rights and tax regulations.