When america began as a nation of thirteen states, the "frontier" was the land between the states and what other boundary? california canada atlantic ocean mississippi river pacific ocean florida

Atlantic Ocean

Explanation:

The Thirteen Colonies were on the east coast of North America. They were: Massachusetts, New Hampshire, Rhode Island, Connecticut, New York, Pennsylvania, New Jersey, Delaware, Maryland, Virginia, North Carolina, South Carolina and Georgia. Therefore, they were all between the Atlantic ocean and the westward border.

yellow fever and other tropical diseases

try this

explanation: