1. Alliances and War
V&H, Chapter 1 (Levy)

2. Introduction
Alliance: A formal agreement among a limited number of countries concerning the conditions under which they will or will not employ military force.

3. COW Alliance Types
Defense pact
Neutrality/Non-aggression pact
Entente

4. Alliance-War Relationship
Alliances make war less likely
Balance of Power theory
Deterrence
They reduce uncertainty

5. Alliance-War Relationship
Alliances make war more likely
They generate counter alliances and arms races
Audience costs
Permanent alliances reduce the number of potential coalitions against the aggressors

6. Empirical Findings
Alliances were associated with peace in the 19th century, but war in the 20th century
Alliances make the expansion of war more likely
Allies are not reliable during war (Sabrosky); allies are reliable during war (Leeds, Long, and Mitchell)

7. Jack Levy’s Study He focuses on Great Powers (GP) from 1495-1975
Interstate wars involving at least one GP (119 total, 64 with GP’s on both sides)
Question: are alliances necessary and/or sufficient conditions for war?

8. Number of Alliances Over Time
Century
16th 17th 18th 19th 20th Total
# of alliances
# of GP
alliances
% GP alliances 80% 56% 93% 56% 15% 39%

9. Necessary Condition Every war (Y) will be preceded by an alliance (X)
Some alliances (X) may not lead to war

10. Necessary Condition
No X (Alliance) X
No Y (War) 45 55 Y 15

11. Sufficient Condition Every X (alliance) will be followed by Y (war)
Some wars may occur when there is no X (alliance)

12. Sufficient Condition
No X (Alliance) X
No Y (War) 35 Y 10 80

13. Levy’s Conclusions
Most alliances were followed by war within 5 years (except the 19th century)
Thus alliance is a near sufficient condition for war in most centuries
However, most wars were not preceded by alliances
Alliances are not necessary conditions for war

14. Alliance Reliability
Do alliance partners come to each other’s aid in war?
Allies do what they promise 75% of the time (Leeds, Long, Mitchell)