Metallica had released four studio albums before its 1991 self-titled album, commonly called The Black Album.
Those earlier records were Kill ’Em All, Ride the Lightning, Master of Puppets, and …And Justice for All. The 1991 album therefore became Metallica’s fifth studio album, a sequence confirmed by its position in the band’s discography.
The progression also tracks a major change in the group’s musical development. Kill ’Em All established Metallica’s early thrash-metal identity, while Ride the Lightning and Master of Puppets expanded its songwriting and atmosphere. …And Justice for All became known for complex arrangements and a notably sparse bass sound.
The Black Album simplified many structures without abandoning heaviness. Its songs were generally more concise, its production more polished, and its singles more radio-friendly. That combination helped the record reach listeners far beyond the band’s original thrash-metal audience while preserving Metallica’s status as a major heavy-metal act.