Heavy metal entered the 1990s with its foundations shifting beneath it. The commercial hard-rock boom had not yet disappeared, but the underground was becoming heavier, more technical and increasingly international. Thrash reached one of its creative high points, death metal developed distinct American and European identities, power metal grew more ambitious and a Texas band found a crushing groove that would influence the entire decade.

Megadeth’s Rust in Peace was the year’s technical thrash summit. The arrival of guitarist Marty Friedman and drummer Nick Menza completed what many fans consider the band’s classic lineup. “Holy Wars… The Punishment Due,” “Hangar 18,” “Tornado of Souls” and “Five Magics” combined precision, speed and complex arrangements without losing their hooks. Dave Mustaine finally had musicians capable of realizing his most demanding ideas, and the result became one of thrash metal’s defining records.

Judas Priest answered the new generation with Painkiller. New drummer Scott Travis opened the title track with a thunderous double-bass assault, while Rob Halford delivered one of his most extreme vocal performances. Glenn Tipton and K.K. Downing sounded revitalized throughout “Night Crawler,” “A Touch of Evil” and “Between the Hammer & the Anvil.” Slayer’s Seasons in the Abyss found the ideal middle ground between the speed of Reign in Blood and the slower menace of South of Heaven. “War Ensemble,” “Dead Skin Mask” and the title track made it an immediate classic.

Anthrax became darker and more serious on Persistence of Time. Songs such as “Time,” “In My World” and “Keep It in the Family” replaced much of the band’s earlier humour with anxiety and social tension, while its cover of Joe Jackson’s “Got the Time” added a burst of nervous energy. Together, the Megadeth, Slayer and Anthrax albums formed one of thrash metal’s strongest single-year runs.

Pantera’s Cowboys from Hell signalled another change. Although technically the band’s fifth studio album, it was their major-label debut and effectively introduced the Pantera recognized by most metal fans. Dimebag Darrell’s enormous riffs, Vinnie Paul’s precise drumming, Rex Brown’s low-end power and Phil Anselmo’s commanding voice transformed “Cowboys from Hell,” “Domination” and “Cemetery Gates” into the foundation of groove metal.

Death metal was evolving just as quickly. Entombed’s debut Left Hand Path established the distorted buzzsaw guitar tone associated with the Swedish scene. Death’s Spiritual Healing moved Chuck Schuldiner toward more technical music and socially focused lyrics, aided by guitarist James Murphy. Obituary’s Cause of Death refined the swampy Florida sound with lead guitar from Murphy and a memorable cover of Celtic Frost’s “Circle of the Tyrants.”

Canada’s Annihilator avoided the usual second-album decline with Never, Neverland, pairing Jeff Waters’ precise riffs with new vocalist Coburn Pharr. Germany’s Blind Guardian expanded its speed-metal roots on Tales from the Twilight World, using fantasy literature, layered vocals and melodic guitar work to advance European power metal. Beyond this Top 10, Queensrÿche released the commercially successful Empire, Alice in Chains introduced a darker Seattle sound on Facelift, and albums from Testament, Kreator, Deicide, Cannibal Corpse and Suicidal Tendencies showed how many directions metal could now travel.