Why doesnt america and other continents print their owm money

Because United States notes no longer served any function not already adequately met by Federal Reserve notes, their issuance was discontinued and, beginning in 1971, no new United States notes were placed into circulation.

This is because most of the valuable things that countries around the world buy and sell to one another, including gold and oil, are priced in US dollars. So, if the US wants to buy more things, it really can just print more dollars. Though if it printed too many, the price of those things in dollars would still go up.