The Changing Nature of Military Alliances
Only six dyads remained allied after the end of World War I,
but the percentage allied increased gradually during the inter-
war period. Then, between 1935 and 1939, the percentage of
dyads that were allied jumped from 30 percent to 80 percent.
The wartime alliances ended following World War II, but the
number of alliances began to increase gradually as the cold war
intensified. By 1960, the percentage of the states of the world
that was allied (67.78 percent) was greater than the percentage
allied in 1945 (63.38 percent). While the number of alliances
continued to increase throughout the cold war years, the third
line on Figure 1 indicates the magnitude of the effect that
NATO and the OAS have had on the system. In many years,
more than half of the allied dyads in the international system
could be found in just these two alliances.
With or without NATO and the OAS, however, almost all
states in the international system have been allied with other
states for at least some period of time. Although initially con-
centrated in Europe, alliance behavior has become a global
norm. Figure 2 examines these data by region. Dividing the
world into five separate regions (Europe, Middle East, sub-Saha-
ran Africa, Asia, and the Western Hemisphere), Figure 2 charts
how many states in each particular region have had experience
with alliances. Thus, for example, Figure 2 shows that Europe by
1720 had fifteen states that had previously been involved in an
alliance; this number grew to more than thirty by 1990.
There are some interesting trends in the regional data for
alliance experience. First, alliances are clearly a European inven-
tion, beginning with the Anglo-Portuguese alliance (Alliance
no. 1.1000) and with a trend that gradually increased during the
eighteenth and nineteenth centuries. The various dips in the
trend line are caused by states that existed in the system at vari-
ous times; these data show that alliance formation does not
always guarantee state survival.
Alliance-making practices spread from Europe to the New
World, as states of the Western Hemisphere began to form
alliances in the mid-nineteenth century. Fifteen states had
alliance-making experience before World War I, and by World
War II, this number had increased to more than twenty. After the
signing of the OAS alliance, there were more than twenty-five
states with alliance experience by the final stages of the cold war.
Asia and the Middle East developed similarly in terms of
alliance practice, as both regions began moving toward inde-
pendence and statehood at the start of the twentieth century. In
Africa, the large regional alliances that were formed after most
of the states in the region gained independence account for the
dramatic increase in the African trend line after 1960. By the
early 1980s, almost thirty African states had taken part in at
least one alliance.
Alliance practices began in Europe and will probably always
be associated with the diplomatic history of that continent,FIGURE 1 Number of Dyads Allied in the International System, 1816–2000