Goats are obstreperous creatures, but when one called Kare disappeared in the wilds of central Sweden in the ninth or 10th century and returned a few days later with horns stained red, no one could know a train of events had been triggered that would still be unfolding today.

In pursuit of greener grass or more goat-like biological urges, Kare had stumbled into a huge copper deposit. It would be mined for a millennium by Stora Kopparberg (Swedish for "great copper mountain"), possibly the oldest company still operating in the world.

Stora's extraordinary history - at different stages its miners fought for and against Swedish kings - is bound up with the fortunes of the Swedish nation. Yet Stora is now neither a miner nor Swedish. In 1998 it merged with Enso to become Stora Enso, a multinational paper manufacturer headquartered in Finland with operations in 35 countries.

  Stora Enso (formerly Stora Kopparberg, a Swedish copper mining company) is now a multinational paper manufacturer

Stora's journey is a thread running through David Rothkopf's sprawling Power, Inc, a thought-provoking account of the shifting balance of religious, secular and private power down the ages, and in particular the emergence centre stage of big business. Stora's interlinked lessons are exemplary here and are ones that the world is struggling to absorb.

Although many fall by the wayside, companies can be, and sometimes to all intents and purposes are, immortal. Their purposes can change and their ultimate allegiance is not to states or any other external power but to themselves.

The irony is that for most of their history, corporations have been the instrument of other, senior sources of power - first religious (Stora's earliest recorded share transfer, in 1288, was between a bishop and his nephew), then state, when crowns "nationalised" religion during the Reformation and the nation state emerged as the primary unit of power. States granted charters to companies to further their economic ends. Britain outsourced the running of large parts of the empire, including India, to the British East India Company.

Even when limited liability was generally adopted in the 19th century (to the disapproval of some who warned of the dangers of corruption) it was not of right but because of the expected collective, rather than individual, benefits.

But without our noticing, the boot has moved to the other foot. In a world where global markets are the ultimate arbiter of policy, the shadow banking system spews out derivatives and other money substitutes that dwarf official money supplies, and companies export employment, profits and headquarters at will, few nation states can claim to be "sovereign" in the conventional sense. In this world, around 2,000 private "supercitizens", as Rothkopf describes the largest multinationals, are fitter for today's purpose than all but 30 or 40 states.

Flourishing in the areas governments cannot reach, using their mobility to play off states against each other, companies have further tipped the scales in their favour by working to transform the privileges granted in the name of the common good - limited liability, immortality, unlimited size - into rights that regulators mess with at their peril.

The spearhead of the corporate transformation from servant to master has been the increasingly aggressive assertion of corporate personhood. Its apotheosis was the 2010 Citizens United case in which the US Supreme Court not only allowed companies the same right to free speech as individuals but also ruled that to restrict that right was unconstitutional.

The issues surrounding the rise of private power are posed most urgently in the US, where legal enablement coupled with corporate determination to retain its privileges has turned the presidential election into a contest between two slightly differing agendas for business, with the winner probably to be decided by whosoever raises the most money from interested parties.

But the shifting interface between public and private power raises many more questions. How, for example, can "loose" centres of corporate power be reconnected to the world they affect so deeply? Can the markets be "greened" so that growth can be achieved without using human lives or the environment as fuel?

Business school theories have played a part in bringing this new world about: how does the academy theorise - and teach - what is happening now? How, for example, do we think about leadership in a post-sovereign world where countries are only partially in charge of their own fate and companies have grown not just too big to fail but possibly also too complex to manage? That goat has a lot to answer for.