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.

what are the others?

union blockade

explanation:

the union blockade in the american civil war was a naval strategy by the united states to prevent the confederacy from trading.

the blockade was proclaimed by president abraham lincoln in april 1861, and required the monitoring of 3,500 miles (5,600 km) of atlantic and gulf coastline, including 12 major ports, notably new orleans and mobile. those blockade runners fast enough to evade the union navy could only carry a small fraction of the supplies needed. they were operated largely by british citizens, making use of neutral ports such as havana, nassau and bermuda. the union commissioned around 500 ships, which destroyed or captured about 1,500 blockade runners over the course of the war.