The book, better referred to as a treatise, is a scholarly work on Professor Mearsheimer's offensive realism theory. The author does well in explaining this highly pessimistic and machiavellian construct structurally and clearly. Professor does not mince words in the slightest. There is no equivocation or obfuscation, which is so commonplace in most social science books. Historic anecdotes are exciting and appropriately used in conjunction with a variety of propositions and sub-propositions within the overall framework.
In other words, the author should get perfect marks for explaining his highly original ideas lucidly. He provides a great example of how a scholar should conduct his or her work in designing a comprehensive theory, explaining its components, using supportive evidences, and contrasting and criticizing rival theories. The author excels in converting highly academic work into something informative and entertaining for non-experts. All this makes going through the work a delightful experience.
And yet, this is not sufficient to make the theory either good enough for practical armchair analysis or good enough as an efficient, let alone moral or ethical guide in current times for most political or policy leaders.
As hinted before, the theory is extraordinarily pessimistic as it takes a dim view of humanity's collective objectives when grouped and divided as nation-states. On flimsy grounds, the author insists that when divided along such lines and without an over-arching disciplining, supra-national, global force, nation-states cannot but view each other with suspicions and doomed to fight merely to survive.
In the author's mind, any liberal or other ideals are mere chimeras behind which leaders of the "greatest" nation-states plot their expansionist agendas. Implicitly, the author seems to imply that if there are any political or military leaders with genuinely non-expansionist or altruistic visions, they will never have a sufficient impact on the global geopolitics. If any nation is unfortunate enough to have some ideologues taking over, such a society will at least temporarily cease to be a "great" nation as per this theory. There will be other ideology-free entities around which will suppress such weak countries who opt out of any expansionist ventures.
There are three significant issues with this theory:
Historically, the theory appears more valid than it is because of the ability to explain geopolitics of the colonializing (and earliest industrial revolution beneficiary) powers in the pre-tech era.
The theory is remarkably static. Its obsessive focus on land-based power grab - reflected in its definition of relative strength, recommended strategies, forecasts - ignore the new power vehicles of the post-industrial era. These new realities not only necessitate new methods within the theory but destroy the fundamental non-liberal, military-expansion driven construct from its roots.
The author fails to realize the vicious circularities that would be created, leading to possibly an eventual extinction of the whole humanity, if everyone explicitly believes in offensive realism as the only way to survive and feels no need to have any other values or ideals.
Let's explain these three in more detail, although not necessarily sequentially.
The author never entertains the thought about the context where offensive realism might not be applicable. If he had started with a simple thought experiment, he would have recognized its universal invalidity until the onset of the industrial revolution. More importantly, it would have led to the conjecture that the same could be less applicable in international geopolitics forever from roughly the publication date of the book (published just before 9/11).
Post-agrarian, pre-tech period of our race is only a phase of our existence. The industrial revolution caused a material change in the way the societies interact within themselves and with each other. Over time, they obliterated kingdoms, fiefdoms, and old power structures as the urbanizing world became a conglomeration of nation-states.
The book is about international interactions, rivalry, and feuds in a particular era, facilitated by industrial revolution innovations, not yet upended by recognition of universal human values, information era derivers/drivers, and marked by the forces of colonization. Starting with the assumptions that go into the makeup of the theory to nearly every example used to bolster the case, the author refuses to look towards a possible world that may not be about its baddest and biggest powers feuding in a land grab.
Despite the various religion-based reformations in societies across the world for the previous two thousand years, there was no concept of equality or human rights until the end of the eighteenth century. There was massive progress on these fronts from the 1770s until the end of the twentieth century. Still, almost all the major actors on the world stage were racists, sexists, chauvinists, feudalists, power-obsessed or religious fanatics because of the value systems of those eras.
With the industrial revolution, the early innovators felt the need to use the new powers to extend their domination that was just not possible in previous times. What expansionists like Alexander or Ghenghis Khan could not do, i.e., hold on to - and not just conquer - vast stretches of faraway land as a prized possession, suddenly became possible. More importantly, with larger dominion, colonizing powers got bigger markets and could build a more significant resource base for even more territory and innovation.
The author's definition of "the great powers" of the past three centuries is tautological. It excludes large nations like China that were insular, India that was colonized, or civilizations like Islam that had opted out. Effectively, the author's great powers were early industrial innovators seeking to protect their innovations from other industrial innovators and competed with them for more resources and markets.
These nations fought bitterly and nearly endlessly for two centuries from the 1790s. Offensive realism is right when it states that the way the nations feuded in international space did not correlate with their domestic political ideologies in this pre-information era. However, the author is not only overly pessimistic and static but also willfully blind to the rise of material new forces over the last fifty years.
9/11 showed how new enemies do not need to be nation-states. Information fluidity shows how innovations cannot be suppressed for as long as before. People on the ground are more aware and less acceptable to blatantly evil state acts on alien societies. Most importantly, in the world of viruses, nuclear bombs, robots, and AIs, infantry/military are becoming less and less critical in the power games.
The biggest problem with offensive realism is that it is one of those theories that, if true, should be roundedly and comprehensively eradicated rather than accepted, as the author suggests. No thinking human should nod a philosophy that demands stronger nations to go out there and dominate with the weaker merely accepting their fate. Any world where ideologies are acceptable ruses for the strongmen of the era to justify killing millions - because that's what international geopolitics is as per offensive realism - would be a sad place. Offensive realism would oppose any attempts at reforming such a system, as the author strongly believes that the best in international geopolitics would be those who follow its guidelines. Believer of offensive realism, like believers of many heinous theories like euthenics, need to be resisted. Otherwise, their arguments will lead to every nation or group justifying its own Hitler equivalent. The author is not just wrong, but he cannot be accepted as right.