These two volumes compile and describe in detail every inter-
state formal alliance signed since the Peace of Westphalia in
- There are more than 450 alliances from 1648 to the pres-
ent that meet the criteria of formal interstate alliances, and for
each case commentary is provided in the form of several para-
graphs on the background and history surrounding the forma-
tion of the alliance as well as, in some cases, the effects of the
alliance on the region or international system. In addition,
commentary often notes when states joined or left an alliance
and when (or if ) the alliance was abrogated. This detailed com-
mentary supports the actual text of the alliance, if available in
English, or an English translation of key alliance terms if no
English text is available.
This book is intended for students, researchers, and casual
readers as well. For students, the case descriptions and the
treaty texts should provide an important supplement for many
graduate and undergraduate classes in international relations
and diplomatic history. For researchers, the commentaries
often include discussions of key coding decisions, and the treaty
texts will provide a single resource for invaluable information
on all international military alliance commitments. Finally, for
the casual reader, the summaries are written in a nontechnical
style intended to guide the reader who is trying to understand
the historical importance of particular alliance treaties.
What follows in this chapter is an introduction to the book
that is organized around the central question that has moti-
vated the majority of alliance scholars:How do international
alliances affect the prospects for war?The introduction begins by
defining what scholars mean by the term military alliance and
then describes the historical debates that have associated
alliances with both peace and war. The collection of alliance
data, such as the data set included in this volume, has been the
key impetus for alliance scholars to move beyond impassioned,
anecdotally driven debates that resolved few questions. When J.
David Singer and Melvin Small introduced the first alliance
data in 1966, scholars were finally able to systematically test the
effects of alliances.
Although a great deal of knowledge about alliances has been
amassed in more than forty years since the first systematic
study, problems persist in the research on alliances. One of the
central problems of alliance research is that scholars have not
adequately considered that alliances vary substantially as a
class. Thus, the final sections of this introduction describe sev-
eral different ways of conceptualizing alliances, including one
framework based on the characteristics of the states making an
alliance and one framework based on Singer and Small’s origi-
nal typology of alliance terms. A short guide to the entries in
these volumes is provided in the section on how to use this
book that follows this introduction.What Is an International Alliance?
An alliance is a formal contingent commitment by two or more
states to some future action. The action involved could entail
almost anything—detailed military planning, consultation dur-
ing a crisis, or a promise by one state to abstain from an
upcoming war. Once reached, the agreement is usually in writ-
ten form and is made public to other states in the system at the
discretion of the states making the alliance. Though less impor-
tant today, secret alliances and commitments have affected the
outcomes of many crises, battles, and wars. For example, the
Hitler-Stalin pact (1939), with its many secret accords, immedi-
ately sealed the fate of the much weaker Poland.
Alliances have been widely discussed by students of interna-
tional relations because hundreds or perhaps thousands of
interactions may take place between states in any given year, but
few interactions create the impact meted out by alliance forma-
tion. This impact allows alliance behavior, unlike most other
forms of international actions, to be quite open to systematic
investigation (Singer and Small 1966, 1). Despite the ease of
tracing these actions, however, researchers have often disagreed
over what constitutes an alliance commitment. Issues of trade
and legal reciprocity are often ignored even though these may
constitute a large portion of an alliance relationship (Ward
1973), and alliances never formalized by treaty are omitted
from most alliance data sets.
Although conceptual problems persist, empirical studies
have developed a consensus that operationalization of the
alliance variable depends on two factors. First, alliancexlixIntroduction: Research and Methodology