[6][7] While there are some precursors to the concept of death metal fused with metalcore/hardcore elements seen in the 1990s, deathcore itself emerged in the early 2000s and gained prominence beginning in the mid-2000s within the southwestern United States, especially Arizona and inland southern California, which are home to many notable bands and various festivals.

Deathcore's expansion in the mid-2000s saw bands like All Shall Perish, Through the Eyes of the Dead, Bring Me the Horizon, Suicide Silence, Carnifex, Job for a Cowboy, Chelsea Grin and Whitechapel taking off.

[6][12] Like in other extreme metal fusion genres, deathcore guitarists down-tune their guitars to give their music a heavier sound.

"[29] Embrace the Eternal (1998) by Embodyment, Yesterday Is Time Killed (1999) by Eighteen Visions, and Rain in Endless Fall (1999) by Prayer for Cleansing are early examples of albums that feature a metalcore sound combined with death metal influences,[30][31][32] in 2019 music site The New Fury has even gone on record to credit Embodyment as "[pioneers] of the deathcore genre" due to their performance on Embrace the Eternal.

"[35] The Belgian H8000 music scene was also influential to the development of the sound, with bands like Deformity, and Liar helping to pioneer a prototype for the genre in the late-1990s and early-2000s.

[37] Death metal bands like Dying Fetus, Suffocation, and Internal Bleeding were influential on deathcore due to their use of "crushing, mid-paced grooves and breakdowns", according to Lawson.

[37] Despite a few earlier metalcore/death metal hybridizations, Antagony[38][39] and Despised Icon are considered to be the true pioneers of deathcore,[40][41] however both bands have rejected the label.

Deadwater Drowning's 2003 EP was remarked as "basically the blueprint for every current deathcore band out today,"[45] while All Shall Perish's debut album Hate, Malice, Revenge (2003) "never got tied down to [simply] death metal or metalcore.

[48] The genre saw an increase in popularity even further when English band Bring Me the Horizon released their deathcore debut full-length Count Your Blessings in 2006.

[53] This wave led Japanese band Dir En Grey to return to their nu metal influence sound while also embracing deathcore on songs such as "Different Sense".

[58] Their third album A New Era of Corruption sold about 10,600 copies in the United States in its first week of being released and peaked at position number 43 on the Billboard 200 chart.

On top of their non-stop touring, the band's methodical songwriting resulted in Carnifex quickly getting signed to label Victory Records.

[74][75][76] French band Betraying the Martyrs has been described as "[the] punishing brutality of deathcore with melodic flourishes pulled from symphonic and progressive metal, giving it a theatricality that feels distinctly European.

The established traditions were being tinkered with, old rules were being broken, and, having already lost out to Slipknot, it was now seeing its ideas taken and warped by a younger generation that was reaping the financial benefits.

"[85] In a 2012 interview, former Chelsea Grin guitarist Jake Harmond said, "Everyone likes to flap their jaw and voice their own opinion how 'embarrassing' it is to be in a band that can be labeled 'deathcore,' but honestly we have never given a fuck".