Why do we use Money? Why not a Barter System?

-A Barter System is when Goods are swapped for other Goods eg Guns for Butter. This is Inefficient as it takes Lots of Times for Traders to successful Barter -Money acts as a Medium of Exchange - both Buyers and Sellers Value, which allows Nations to buy Goods even if Sellers don't want whatever the Nation produces. Exchange Rates are also Important here.