With The Joshua Tree, the U2 pendulum swings back to America again. If The Unforgettable Fire, partially through Brian Eno’s guidance, was their most European record, this, their fifth studio album, turns their sights again on the Big Country, sometimes howling off in pursuit of the ghosts that possess the American soul. In time, it may be reckoned their most influential album to date.

It also clarifies how U2’s vocation has become the revival and renewal of rock and the recovery of its most romantic values. Between the increasingly mercenary implosion of hard rock into a static vaudeville routine and the intervention of pop dance-floor values, rock has lost its lustre and mystique of genuinely redeeming passion.

From one angle, The Unforgettable Fire can now seem a strategic retreat, to regroup, reassess the situation and gain new ammunition. But if that album necessarily circumvented some of the issues, The Joshua Tree returns to a frontal assault.

It is also the second successive album where U2 strip away the skins of their previous styles. Only the opening ‘Where The Streets Have No Name’, ‘In God’s Country’ and, possibly, elements of ‘One Tree Hill’ preserve previously identifiable hallmarks. Otherwise, The Edge’s guitar has developed its own military tendency, homing in on the legacy of Jimi Hendrix and Led Zeppelin, while the group’s new commitment to songs finds both Bono and the rhythm section contending on dance-floors they never previously frequented, with complete confidence.

For, stylistically, the triumph of this album is that, like Prince, U2 prove an act can still be contemporarily commercial and also capture the higher ground. There’s a host of unexpected influences here but they’ve been discriminatingly used, to release rather than imprison the band. The effect is to release rock also from its own self-imposed shackle, for, in the process of resetting their sights, U2 unravel a series of musical problems, other less resolute souls have abandoned for cliche.

Twice, they almost teeter on the brink. Both ‘Red Hill Mining Town’ and ‘I Still Haven’t Found What I’m Looking For’ are more obviously singles than anything previously released bar ‘Pride’, but the first is perilously close to Bon Jovi in its scarf-waving melody, while the latter is destined to provoke comparisons with Rod Stewart – albeit before that singer’s career became an endless audition for Dynasty and Miami Vice.

Bon Jovi and Rod Stewart? To some, this will sound like I’m excusing a crude sell-out. That isn’t true at all, for two reasons. First, because Bono has never before sung with such emotional accuracy. And secondly because this is a most deceptive album, simultaneously swimming into the mainstream and then recoiling from its most repellent values.

For if the music is pro-American, the message hardly is. For instance, if ‘Red Hill Mining Town’ initially sounds like potential standard MTV fare, its lyric about an unemployed and dispossessed mining family definitely isn’t. Thus The Joshua Tree consistently shifts targets and expectations.

But, then, U2’s own perspectives have also shifted. The Joshua Tree may be the first album where U2 have dared to let the demons loose in the studio, the one where ultimately all the issues of religious faith seem as complex and clouded as they really are. On ‘Exit’, both the guitar and rhythms convey a brooding premonition, as Bono tells the tale of one of those psychotic saviours with warped interpretations of the Old Testament, a murderer slaying with “the hands of love”. Here, U2 finally confess their gradual recognition of the Anti-Christ in everybody.

For faith is no longer what once it seemed. ‘I Still Haven’t Found What I’m Looking For’ is all its title says, U2 gone soul and gospel but admitting doubt and restlessness. Elsewhere certainties become conundrums: “Sleep comes like a drug... sad eyes crooked crosses... In God’s Country” (America not Ireland – foreign correspondents please copy) boasts a powerful ambiguity: ‘Bullet The Blue Sky’, “Plant a demon seed, you raise a flower of fire / See them burning crosses, see the flames, higher and higher”.

This last track is where U2 really cut the cable. The fourth track into the first side, on it The Edge releases a dirty, furious wall of sound under remorseless, lockstep rhythms, these musical dramatics in service to a scenario that’s located somewhere in the killing fields of Central America. A key track, where U2 rubbish heavy metal conformity, it could also become this year’s ‘Bad’, the spontaneous combustion centrepiece of the tour as Bono lets fly with a rap about a tempter “peeling off those dollar bills”.

Its violence also underscores the difference between this album and its predecessor. For if The Unforgettable Fire’s airier textures seemed to evoke the more celebratory, mystical aspects of belief, The Joshua Tree finds U2 as worried, even frightened, men grappling with the moral burdens of suffering, culminating in the closing track, ‘Mothers Of The Disappeared’, about the victims of state terrorism, and patently inspired by last summer’s American benefit tour for Amnesty International.

Could and should their politics be more explicit? It depends on your perspective. U2 presently content themselves with a liberal moralism that’s alert both to how planet pop limits local language and the fact that their potential American constituency cannot, by any stretch of the imagination, be equated with NME readers. But even if the sheer force of U2’s music dramatises their parables, as a lyric-writer, Bono may still be erring on the safe side of coded ambiguity.

Of course, there’s more to The Joshua Tree. ‘Trip Through Your Wires’, once an unruly debutante on TV Ga Ga, has been disciplined into a Dylanesque stomp, with Bono let loose on harmonica, while another love song and possible single, ‘With Or Without You’ has perhaps his most controlled vocal, building from an almost conversational first verse over a bare rhythm section to a soul-baring confession.

“And you give yourself away,” he sings – a line which may be the key to the U2 ethos, to the heart of a band who have consistently preached their own brand of self-surrender. This album may be scattered with references to the desert but, in this dry and waterless place, U2 would also be at one with AI Green in singing ‘Take Me To The River’.

That river returns on ‘One Tree Hill’. Dedicated to their Maori roadie, Greg Carroll, killed in last year’s motorcycle accident, it starts with light, glistening, almost African guitar from The Edge, over Adam and Larry’s own amendment of tribal rhythms, with the guitar becoming increasingly aggressive through the song. But ‘One Tree Hill’ is hopeful. “We run like a river to the sea,” Bono sings, Mike Scott’s metaphor recast in terms of eternal life and the Maori’s own belief.

Once again, U2’s religious romanticism becomes the source of positive values. More secularly-minded people may think this preposterous but U2’s religious impulse – closer to Sufi lore, based on love not dogma, preferring the kernel to the shell of formalism – is curiously capable of reviving the old skin of dead rock ceremonies that, as a secular substitute for religion, have patently degenerated this decade. Somehow they continue to evade the traps.

The Joshua Tree rescues rock from its decay, bravely and unashamedly basing itself in the mainstream before very cleverly lifting off into several higher dimensions. They’ve been misunderstood occasionally, even by their committed supporters – but after The Joshua Tree, with its skill, and the diversity of issues it touches, one thing is absolutely clear: U2 can no longer be patronised with faint and glib praise. They must be taken very seriously indeed after this re-evaluation of rock.