Philip II of Spain was one of the most hard-working monarchs in 16th-century Europe.

He spent hours poring over official correspondence, or granting audiences to the endless line of petitioners banging on his door. There is a difference, of course, between working hard and working efficiently. As someone grumbled in 1584, Philip wanted "to do and see everything, without trusting anyone else, busying himself with so many petty details that he has no time left to resolve what matters most".

As Geoffrey Parker explains, this was a perilous strategy because there was an awful lot of business to be conducted. Philip's territories ranged from Iberia, parts of Italy and the Low Countries to distant enclaves in Asia and the Americas. He ruled over tens of millions of people, and the world had not seen such logistical problems or complex budgets since the days of the Roman Empire. Philip would have made for a conscientious constituency MP. As king of Spain, he should have learned to delegate.

What, though, was the source of all this misdirected energy? Parker's book leaves us in no doubt that Philip thought very highly of himself. The phrase "messianic mindset" is deployed and it is not far wide of the mark. Philip was fully convinced that he was privy to the Almighty's plans and, therefore, the only man for all the important jobs. He once wished a minister good health and a long life so that he could remain "engaged in God's service and in mine, which is the same thing". Such self-confidence could have disastrous results. Philip had a bad habit of refusing to draw up contingency plans for even the most important initiatives: what was the point, since everything was destined to go swimmingly? Frequently, it didn't.

Make no mistake, Philip achieved a great deal (from notable military victories to the construction of the Escorial), but his certitude also led to some terrible decisions. From 1571 he became obsessed with destroying Elizabeth I of England. The 1588 Armada, which cost 15,000 Spanish lives and a third of the ill-fated fleet, was simply the high watermark of such foolhardiness. In 1566, Philip decided to scrap the concessions that had been granted to Spain's Morisco population - those subjects of Muslim/Moorish ancestry who had been obliged to convert to Christianity. He decreed that Morisco dress, language and customs were to be abandoned. Revolts ensued and another 90,000 Spanish lives, Christian and Muslim alike, were blotted out.

Fans of Philip II have always had one historical fact in their corner. Most of Philip's 17th-century successors did an even worse job. One wonders, however, if this was largely because of the legacy Philip left behind. He waged a lot of wars, and many of them were unnecessary. He could have sued for peace with the Ottoman Turks quite early in his reign, but this did not appeal. He could have dealt with the Dutch Revolt, which sent Northern Europe into a geopolitical spasms for decades, with much greater finesse, but this did not suit his temperament.

His quest for purity also had parlous consequences. There was, in the context of the times, nothing wrong with a Catholic monarch attempting to stave off the Protestant advance, but Philip went to excessive lengths. He created, in Parker's phrase, a "quarantined" nation which made it difficult for an ambitious student or professor to engage with, let alone travel to, the wider Europe. Finally, he did irreparable damage to Spain's finances and, with all that New World gold and silver flooding in, it took considerable negligence to empty the coffers so efficiently.

There is no Anglophone historian who knows more about Philip II than Geoffrey Parker. In this soaring biography, which draws on a cache of recently discovered documents as well as the enormous back catalogue of archival deposits, he paints a compelling, even-handed portrait of the most powerful man in 16th-century Europe. Parker informs us that Philip's handwriting is hard to read. It is no easier to decipher his legacy. It seems that he didn't kill his son Don Carlos (whatever the Verdi opera tries to tell you) but he was not averse to removing other obstacles. He continues to fascinate -- if you are in the market for a nuanced study bolstered by a lifetime of study, Parker is your man and this is, for me, the historical biography of the year.