Complex sentence: He recovered and joined the Georgia Militia in 1842, became aide-de-camp for the Commander-in-Chief, and commissioned brigadier general of the 2nd Brigade of the 7th Division in 1845.
Split into simpler sentences: He recovered and joined the Georgia Militia in 1842, becoming aide-de-camp for the Commander-in-Chief. Foster was subsequently commissioned Brigadier General of the 2nd Brigade of the 7th Division in 1845.