The 400 Unit debuted in 2009 as the backing band of Americana artist Jason Isbell, an Alabama native who previously performed with the Drive-by Truckers. After making his solo debut with 2007's Sirens of the Ditch, Isbell introduced his new band with a self-titled release, Jason Isbell and The 400 Unit, in February 2009. The record peaked at number 131 on the Billboard 200, received a nomination at the Americana Music Awards, and foreshadowed the success that would follow during the 2010s. After 2011's Here We Rest, Isbell released two records under his own name, including the Grammy-winning Something More Than Free (2015). Meanwhile, he continued touring with The 400 Unit, whose lineup had evolved to include guitarist Sadler Vaden, bassist Jimbo Hart, drummer Chad Gamble, keyboardist/accordionist Derry DeBorja, and occasionally fiddle player Amanda Shires. The group officially returned in 2017 with The Nashville Sound, which peaked at Number 4 on the Billboard 200 and won Grammy Awards for "Best American Roots Song" and "Best Americana Album." The group released a concert recording, Live from the Ryman, in 2018, then returned to the American Top 10 with 2020's Reunions, which also reached the Top 20 in both the UK and Australia. One year later, the group saluted a number of its influences with Georgia Blue, a covers album featuring songs originally popularized by REM, Otis Redding, and others.