When the U. S. colonies gained their independence from England, the was agreed upon as the western boundary of the newly independent country. The land area of the new nation was then doubled shortly afterward with the Louisiana Purchase in 1803.

The Mississippi River.

Explanation:

In the Treaty of Paris of 1863, Great Britain recognized the independence of the United States, ending the Revolutionary War.  The treaty established the US borders with the British territories, with Britain making generous concesssions. The Western boundary was established along the Mississippi River, which was going to be open to navigation by both sides.

the answer is option a.

under god i have placed my chiest strentgh and the safe guard to my loyal subjects