Another fundamental challenge to classical realism and neorealism was the emergence
of the unipolarity of the United States of
the unipolar structure in the international system after the end of the Cold War,
and dissolution of the Soviet Union.
The thing is that unipolarity is perceived as
a highly unusual and unnatural structure
of the international system from the perspective of realists.
Realists believe in the balance,
in the natural tendency of the international system to establish balance.
Whereas, unipolarity is an apex of unbalance in the international system.
However, in reality, the world in 1992,
after the collapse of the USSR really looked unipolar.
The first to declare unipolarity was
the American scholar and journalist, Charles Krauthammer,
who coined in his foreign affairs article in 1991,
the term ''unipolar moment''.
That is describing of the unique moment of international system
emerging after the end of the Cold War.
And at that time,
indeed the United States enjoyed
a vast preponderance over all the other countries in the world,
in the majority of fields of power.
The US was economically very strong,
the US was militarily the sole superpower,
the United States enjoyed universal values,
and exercised universal values.
It enjoyed technological advancement over the other countries,
and was culturally very attractive.
So indeed, no one in the world could be comparable to the United States at that time.
And emergence of this unipolar moment,
immediately triggered debates about how stable and durable will it be.
In other words, whether the United States as the sole superpower,
will be able to ensure international peace and stability,
and prevent or at least postpone a new wave of great power competition.
Liberals did not have problems in explaining this
and agreeing with the unipolar stability.
And in general, liberal paradigm was much better prepared to
explain the fundamental transformations of late 1980s, early 1990s.
They did explain the end of the Cold War,
they did explain the collapse of the USSR,
and they also did explain the unipolar moment.
And argued, and try to prove that unipolar moment,
that US global hegemony was possible, stable, and durable.
Liberal internationalists within the liberal camp argued
that in order for the United States to preserve its hegemony,
it needs to be benevolent,
and exercised multilaterally, which means it should
be exercised through rules and institutions rather than unilaterally.
It should be based on universal values,
cultural appeal, and technological advance of the United States.
And such kind of multilateral benevolent exercise of
the US hegemony will make it more
acceptable and legitimate for the majority of the countries in the world,
and thus the US hegemony will be much more
stable than the previous hegemonies in history.
Neo-conservatives, another angle of the liberal camp,
claim from their perspective that unipolarity is also stable and can be
durable if the United States preserves power preponderance above all the other countries,
above all the rest.
And which is more important from the neo-conservative viewpoint,
uses this window of opportunity,
this unipolar moment to rapidly and resolutely
transform the world in accordance with American values and interests.
Which means for instance, transform rogue states,
countries like North Korea, Iran,
Syria, Cuba, Libya at that time,
Yugoslavia under Slobodan Milosevic,
and others from authoritarian anti-American states to democracies.
So, if the United States conducts
this profound transformation of the international system in a quick and resolute way,
it will ensure stability and durability of its hegemony, and unipolarity.
As for the realists,
they were quite concerned about
this unipolar moment and they had difficulties in explaining it.
In general, the realist camp was split on
the issue of stability and durability of the unipolar moment.
Structural realism, since it considered bipolarity,
not unipolarity as the most stable configuration of international politics,
it claimed that the emergence of these vast disbalance of
the unipolar structure might be even more dangerous than the cold war,
than the age of nuclear deterrence.
This of course sounded quite bizarre,
and to say at least unusual in
the post Cold War period when the majority of people were talking about the era of peace,
the era of prosperity,
the era of integration.
It was bizarre to hear that realists at the same time were
talking that this new age is even more dangerous than the cold war,
when everyone made a sign of relief when the Cold War ended.
To tell the truth, this realist assertion that the unipolar world was much more
dangerous than the bipolar Cold War was quite bizarre at that time.
The whole population made a big sigh of relief when the Cold War ended.
The Cold War resumed a constant threat of total nuclear annihilation,
and in conditions when almost everyone,
or the majority of scholars, observers,
and politicians were talking about the new era of peace,
the new world order,
the new era of cooperation and integration.
Realists, who talked about that this new period in their opinion,
is much more dangerous than the Cold War,
they sounded quite bizarre.
However, they made this case.
For instance, Kenneth Waltz,
the founding father of structural realism, claimed that hegemony,
and he defined hegemony as a single power's possession of
simultaneous economic efficiency in production, trade and finance.
He claimed that this hegemony is the most unstable international structure,
because superiority of one single power would unavoidably cause resistance of the others.
So, according to Kenneth Waltz,
the emergence of unipolarity could result in the war of all against the United States.
Christopher Layne, another prominent realist
argued that the new great powers will emerge soon.
That great power conflict is unavoidable,
it will come rather sooner than later.
And thus unipolarity is not even a moment, it is an illusion.
However, there also were some realists who
accepted the proposition of the unipolar structure,
and claimed that unipolarity could be stable and durable.
Among them, there were Robert Gilpin,
the creator of the so-called liberal hegemonic stability theory,
and William Wohlforth, another very renowned American scholar.
They argued that under certain conditions,
hegemonic predominance may be more stable than the bipolar world.
William Wohlforth, from his position claimed that
unipolar structure was more peaceful and durable than was bipolarity.
Because it prevents great-power competition,
and compels the second tier countries to pursue ''bandwagoning'' strategies,
rather than balancing strategies.
After all, the bipolar structure presumed
a constant contradiction and clash among the USSR and Soviet Union,
they balanced each other,
they competed against each other,
and great power competition was there always.
There was no great power war,
but there was an outright and fundamental great power competition.
And Wohlforth claimed that unipolarity excludes great power competition,
basically because there is only just one great power,
the United States, and that's it.
And no one else can compete with the United States.
No one can challenge the United States in the unipolar structure.
Balancing strategies if they are attempted
by the others against the United States would lead to their destruction.
So, rational behavior excludes balancing,
and the only choice for all the rest is to bandwagon,
which means to join the United States.
And according to Wohlforth,
the United States should conduct active hegemonic policies,
and actively prevent emergence of rivals in order to
keep this power gap between itself and all the rest,
and thus ensure durability of the unipolar world.
And these points were argued in a very famous classical article by William Wohlforth,
Stability in the Unipolar World.
Robert Gilpin from his perspective,
applied the hegemonic stability theory,
which he developed before to the new unipolar realities.
And argued that American hegemony might and should be stable and
durable if it is based on just fare norms and institutions,
and if hegemony conducts self-restraint.
So, you see the propositions,
the advice that Gilpin and Wohlforth gave were opposite.
Wohlforth was talking about the necessity of the US to
conduct a very active hegemonic policies.
Gilpin claimed that the United States should instead conduct restraint.
But, they both accepted the possibility of the unipolar world to be stable and durable.