Although the term "punk rock" has been retroactively applied to 1960s acts like "The Velvet Underground" and "Blue Cheer," the punk movement in music truly began in the 1970s with groups like "The Sex Pistols" in England and "The Ramones" in the United States. In part a reaction to the intricacies and pretensions of psychedelic and progressive rock, punk music was a rock and roll that valued simplicity, directness and aggressiveness over fine musicianship, "artsy" lyrics and beauty.
Hardcore, which began in the 1980s primarily in the United States, took the punk concept and pushed it further. Hardcore bands like "Black Flag," "Minor Threat" and "The Dead Kennedys" tended to play harder and faster than "The Sex Pistols" or "The Ramones," with aggressive vocals and a barreling forward, non-swinging musical style. Lyrics often reflected radical or nihilist political ideals, and intricate musical composition or virtuosic musicianship were frowned upon.
In the 1990s, some groups who had either been part of or influenced by the hardcore milieu began taking the music in a new direction that was eventually labelled emocore, or simply emo. Bands like "Rites of Spring," "Sunny Day Real Estate" and "Braid" continued hardcore's aggressive style, but, as the name of the genre suggests, their lyrical content also expressed emotion. The complex songwriting and emphasis on musicianship disdained by hardcore returned in emo groups.
As the name suggests, in the early years of the twenty-first century, screamo took the basic emo playbook and added an innovation in vocal style. Continuing emo's lyrical turn toward the personal and the emotional, screamo bands like "Thursday," "The Used" and "Glassjaw" alternated between vocals that were relatively conventional, even "pretty," and various flavors of screaming, from high-pitched shrieks to low growls. Although screamo evolved from hardcore, it differs from the classic bands of that style with its introspective lyrics, generally "tight" musicianship and distinctive vocal style.