Heavy Metal...

With heavy metal, the style of Black Sabbath was solidified, but deeply hybridized with the progressive rock, Celtic folk and electric blues fusion of Led Zeppelin, having influences also from aggro-prog bands like King Crimson and Jade Warrior. The late 1960s culminated in rock being bored with itself, and after the Beatles went progressive and British and American blues-rock guitarists aimed for more lengthy, complex works, rock essentially turning progressive in nature. "Progressive" is perhaps a misnomer, as there's no "progress" in re-incorporating influences from classical music, but for rock it was progress from the simplistic pop of the 1950s to incorporate new styles and vastly adulterate the blues framework of rock (the blues is a syncopated version of Celtic and German folk-pop, formed in America of the mixture of cultures; like most popular music on all continents, it features easily transposed chord progressions and a basic song structure which allows easy melodic improvisation).

This music, tame as it sounds today, was a turd in the punchbowl among the progressive and folksy, mostly pacifistic and hedonistic rock of the time. Unlike the good times and party hearty vibe of most music, metal, like dissident apocalyptic rockers the Doors before it, was "heavy" in that it took on weighty existential topics and its partying was self-destructive, an expression of impending doom. It was not happy fun include everyone music; it was for darker souls, those more likely to strike out in anger at the world, and those who felt a need to reject more than embrace recent social changes. Consequently, it embraced dark imagery, with Iron Maiden taking on occult topics, Motorhead wearing Iron Crosses (a symbol of the defeated National Socialist regime in Germany), and Judas Priest not only writing songs about WWII but openly accepting a demonic, warlike persona.

Alone this would be cause enough to say metal was divergent from rock of the time, but the musical factor of its development was important. Unlike the harmony-based, short-cycle riffs of rock, metal almost exclusively used moveable power chords, which can be played in any position along the neck of the guitar in quick sequence, thus lending to riffs written as phrases (like classical, or jazz) more than rhythmic variations built around open chords. This both simplified the music to the point where it was highly accessible, and gave it a dark sound which lent itself, as in classical composition, toward a narrative song structure in which riffs form motifs that resolve themselves over the course of a song. While clearly much of the heritage of this style comes from the lengthy classical-borrowing epics of progressive rock, between the raw nature of the inverted fifth and the thunderous effect of chordal phrases buffeting the listener, it produced a gnarled, feral sound.

Even more alarmingly, for those who wanted to immerse themselves in the hippie pop of the time, metal was openly embracing of the wilderness (similar to the concept of "the frontier" in the music of the Doors) and replaced a desire for moral certitude with a desire for the lawless. Its musicians wrote about ancient times, about battle and death, and seemed to be searching through the haze of the counterculture for something of eternal meaning, which explains to some degree the vast amount of ecclesiastical and occult symbolism in all metal bands of the period. Indeed, in Venom and Angel Witch and many other NWOBHM (New Wave of British Heavy Metal) acts, there was an almost exclusive focus on the dark side and on the spiritual figures society rejected for not being tamed, such as Lord Satan himself.

Using occult imagery to reflect political topics was also popular, and is best exemplified by what became the prototype of all "Satanic" metal lyrics to follow, Black Sabbath's "War Pigs"

Generals gathered in their masses,
just like witches at black masses.
Evil minds that plot destruction,
sorcerers of death's construction.
In the fields the bodies burning,
as the war machine keeps turning.
Death and hatred to mankind,
poisoning their brainwashed minds.
Oh lord, yeah!
Politicians hide themselves away.
They only started the war.
Why should they go out to fight?
They leave that role to the poor, yeah.
Time will tell on their power minds,
making war just for fun.
Treating people just like pawns in chess,
wait till their judgement day comes, yeah.
Now in darkness world stops turning,
ashes where the bodies burning.
No more War Pigs have the power,
Hand of God has struck the hour.
Day of judgement, God is calling,
on their knees the war pigs crawling.
Begging mercies for their sins,
Satan, laughing, spreads his wings.
Oh lord, yeah!
In this song, a humanity distracted by political and monetary concerns turns its back on reality, thus a travesty occurs and is unnoticed by all while, in the last verse, the demonic figure of hatred and death triumphs.

Heavy metal grew prodigiously from 1972 to just after the turn of the decade, and at that point was replaced by newer styles which represented a re-infusion of hardcore punk styles; unlike punk, hardcore punk did not follow pop song structures nor did it use conventional harmonics, often consisting of two or three power chords per song, rhythmic and droning riffing, and songs that like small operas were built around their own topics. If a song was about death, it might end abruptly; a song about war might diverge into a middle interlude with no immediate relation to the previous works. What drove hardcore punk was the insistent pace of its music, and the power chord phrases that resembled the topics of each song much as each song's structure resembled the topic being discussed. Lyrics and music were united. However, hardcore was quite simple and soon drowned in a sea of imitators.