In 1768, James traveled over the Allegheny Mountains to Westmoreland County, Pennsylvania, where he settled near the Monongahela River, neighboring Redstone Old Fort. It's likely that James and his brother William helped build Williams Cabin near Old Bedford Village, in Bedford County, Pennsylvania. In 1774, Brenton was commissioned a Captain by Colonel Angus McDonald, who mustered roughly 400 men to take part in the Wakatomica Campaign of Dunmore's War. The Shawnee settlements of Wakatomika as well as four other villages were burned. Three American Indian Chiefs were taken prisoner. In 1777, he defended the frontier, serving as a First Lieutenant in the Virginia Rangers of Monongalia County. In 1779, he was promoted to Captain, and then to Major by Patrick Henry. Later that year, James and his family relocated to Harrodsburg, Kentucky County, Virginia. They spent the winter in Harrodsburg, and in spring of 1780 settled on the south bank of Clarks Creek at the ford northeast of Danville. In 1782, Brenton was commissioned a Major and made fifth in command of the Crawford Expedition, intended to put an end to Indian attacks on frontier settlers. James Brenton was one of four majors elected for the expedition. The other Majors included David Williamson, Thomas Gaddis, and John McClelland. According to Consul Willshire Butterfield, Major Brenton, "was a man of much spirit – a soldier, brave and active. Judging of his merits by his subsequent conduct, he unquestionably commanded the esteem as well as the confidence of the volunteers. His coolness and bravery in the face of imminent danger were long after alluded to by his surviving comrades, in terms of the highest commendation." Major Brinton and Captain Bean were also scouts; observing two savages, upon whom they immediately fired, though without effect. Brenton was wounded at the Battle of Sandusky and Daniel Leet subsequently took command of his division.
The song, "Crawford's Defeat by the Indians" mentions Major Brenton: Shortly after returning from the Crawford Expedition, Brenton was mortally wounded at the Battle of Blue Licks on August 19, 1782. One of the last battles of the AmericanRevolutionary War, Blue Licks took place near the Licking River, in what is now Robertson County, Kentucky. Approximately 50 Loyalists and 300 American Indians ambushed 182 frontier militiamen. James' son, also named James, was in the party which buried the dead after the Battle of Blue Licks. According to family legend, James brought his father's body back to Harrodsburg for burial.
