Burr had fought in the American Revolution, attaining the rank of Colonel at a very young age. He took part in then-American General Benedict Arnold's invasion of Canada in 1775-6 (which failed to capture Quebec City and later withdrew after months of an ineffectual siege) and also was briefly an aide to George Washington. Burr and Washington never got along. .
Burr resigned from the army in 1779 due to ill health caused by injuries and sun stroke mainly from the Battle of Monmouth Court House in New Jersey. He began to practice law and built himself a power base in New York City, founding the first powerful city machine in the new country, Tammany Hall, and later creating a bank for immigrants, housing projects and a safe water supply piped into the city from Upper Manhattan Island.
Burr's "adventures" in the western territories began only after he was left out of hope for the Presidency by President Jefferson, knew he would be dropped from the ticket in the latter's second term, and was defeated for Governor of New York by a Federalist candidate in 1804, helped in part back attacks by Hamilton. Thus it was Jefferson's going back on his bargain with Aaron Burr that led indirectly to the death of the Virginian's old adversary in George Washington's cabinet, General Hamilton.
Dueling was hardly unusual back then ,although it was illegal in the many northern states. The second point is more interesting; exactly what was it that Aaron Burr was up to in 1807 out "west" (i.e., the Trans Appalachian territory of the United States? Did he mean to annex the newest parts of the republic for himself and some of his "Little Band" as they were called, or was he simply anticipating a war with Spain over Texas and Mexico and was headed south to recruit money and ships to take advantage of anti-Spanish hostility? Was he really a traitor (he was never convicted) or simply an adventurer who happened to be mad at Jefferson for not keeping the bargain the Virginian had made in 1800 to support Burr for President after his term (s) in office were over?