Background and production
In June 2013, Megadeth released its fourteenth studio album, Super Collider, to mixed critical reaction. In the months following the album's release, frontman and guitarist Dave Mustaine revealed that he and the rest of the band had already begun to discuss a follow-up, an urgency somewhat influenced by the then-recent death of Slayer guitarist Jeff Hanneman, which had reportedly given Mustaine a sense of mortality.
Over the course of 2014, the band announced its intentions to start pre–production on the album. The band had been working on new material since December 2013, and in January 2014, Mustaine revealed that many riffs had already been written for the record. In May 2014, prior to his departure, Drover revealed that he and Mustaine had entered the studio and began tracking some demo ideas. The band originally planned to record in August 2014 and release the album in 2015. Instead, plans were only made to demo new material that October and start recording in January 2015. Mustaine elaborated that, due to a reduced tour schedule for summer 2014, the band had more time to focus on songwriting.
Additionally, several hardships struck the band in 2014. In May, bassist David Ellefson lost his brother Eliot to cancer, following which, the band cancelled a number of scheduled shows. On October 4, Mustaine's Alzheimer's-afflicted mother-in-law went missing from a campground. Her remains were discovered on November 26. Furthermore, drummer Shawn Drover and guitarist Chris Broderick announced their resignations from the band that November. The pair would later emerge in a new band, Act of Defiance.
Despite everything, Ellefson announced that the band was still intent on starting work on the album in early 2015. Ellefson additionally suggested that the album would "help determine" Broderick and Drover's replacements.
Production and recording
In February 2015, Ellefson revealed that the album was "pretty much written". The band entered Latitude South Studios in Leiper's Fork, Tennessee in April 2015, and recording finished in July. It was initially unclear as to who would produce the album. Mustaine suggested that instead of rehiring Johnny K, who produced both Thirteen (2011) and Super Collider (2013), the band would possibly opt for a new producer. While Mustaine initially indicated an interest in working with producer Max Norman, who had mixed Rust in Peace (1990) and produced Countdown to Extinction (1992) and Youthanasia (1994), it was later revealed that Mustaine would be producing the effort along with Toby Wright. However, Wright was let go early on, and Mustaine instead produced the album with Chris Rakestraw.
While there was initial speculation that Mustaine and Ellefson might try to reunite the Rust in Peace-era lineup, there was initially no statement from the band on the matter. It later came to light that the band had in fact been in discussions with former members Nick Menza (drums) and Marty Friedman (guitar), but were unable to reach an agreement. The opportunity would not arise again, as Menza died of a heart attack in May 2016.
During March 2015, several rock music news websites speculated that Lamb of God drummer Chris Adler would perform drums on the album, which was later confirmed by the band. It was also announced in the same month that Angra guitarist Kiko Loureiro joined the band. Mustaine revealed a track listing for the then-untitled album on July 27 and announced production of the album was completed a month later.
The cover was done by New York artist Brent Elliott White, who was given the idea to go for a post-apocalyptic approach. Vic Rattlehead is depicted as a cyborg, with a virtual reality headset in place of the riveted visor, a headset instead of metal caps on the ears, and a mouthpiece resembling a mask. The pose, holding the head of a cyborg resembling the Statue of Liberty and a katana, is an homage to Seven Samurai. The setting homages 12 Monkeys by having a deserted and destroyed city, Mad Max by putting Vic under the Sydney Harbour Bridge, and The Walking Dead with the "drones meant to be like Michonne’s enslaved zombie buddies". In the 2016 Burrn! magazine Readers' Pop Poll, the cover was awarded Best Album Cover.