74 International Relations Theory of War
to fight each other, as the best way for countries to survive under inter-
national anarchy is to achieve greater capabilities than all other countries
in the system. However, anarchy alone cannot explain why the security
competition sometimes leads to war and sometimes does not, because the
system is always under anarchy, whereas war does not always occur in the
system. To explain this significant difference in the behavior of countries,
the theory adds a systemic variable: the division of power between polar
powers, or the polarity of the system. The theory states that power in an
international system is usually divided in three main ways. Therefore, to
assess the effect of the division of power on the feasibility of war, we must
identify the polarity of the system at each point in time and determine
whether the system is multipolar, bipolar, or unipolar. According to the
book, for systemic theory, the key questions are how changes of the system
affect the frequency of wars,^17 and how changes of the system influence
the intensity of wars. The study implements the three existing structural
models according to the international relations theory of war in evaluating
the stability or belligerent tendency of each of these three systems and
indicates that level of the international system as the key cause of the out-
break of wars involving polar powers. According to the study, each of the
three possible polarity models will affect the stability of the system differ-
ently: bipolar systems will be the most stable, multipolar systems will be
the most destabilized, and, unipolar systems will lie between them.
Confirmation of the argument that the polarity of the system is the fac-
tor affecting the stability of the system is provided by studies developed
from broad databases and that have discussed the various aspects of
wars.^18 The consequences of these studies are very important because only
through empiric studies can we hope that patterns, trends, and possible
causes of the outbreak and outcomes of wars may be identified.
The current subchapter assessed the degree of stability of the three pos-
sible system models by examining all instances of that polarity model in
the period assessed in the study, 1816–2016: two instances of multipolar
systems, 1849–1870 and 1910–1945; three instances of bipolar systems,
1816–1848, 1871–1909, and 1946–1991; and one instance of a unipolar
system, 1992–2016. In the current subchapter, I present the causal expla-
nation of my theory for the events. I ask to examine two key questions:
firstly, how many years of war, the years in which the polar powers were
involved in war, occurred in the three different polarity models; secondly,
how many wars, of the three possible models of war—central, major, or
minor wars—occurred in each of the three different polarity models.
We now turn to the two stages of the empiric assessment of the systemic
dependent variable, stability of international systems. The quantitative
study examines all interstate wars that involved polar powers under the
six instances of the three polarity models in 1816–2016. The purpose of the
assessment is to prove correlation between the assumptions of my theory