Alliance Formation and War Behavior

Point: Alliance formation is not associated with high levels of war.
There appears to be a fundamental difference in the character of alliances.
Alliances before Congress of Vienna (1815) were offensive while after that alliances are defensive
Before, the initiation of military action was explicitly called for in the treaty and not conditional upon an external military attack. In modern treaties, the action triggering the alliance commitment is a military attack against one of the allies.
Contrary to the popular hypothesis that the greater the number of alliances, the greater the amount of war. His empirical evidence shows that historically, periods of high alliance formation have been characterized by relatively infrequent wars, of short duration, low magnitude, severity and intensity.
All great power alliances of the 16th – 17th and 20th centuries have been followed by a war involving a great power within five years.
A very small portion of 19th alliances are followed by great power wars involving one or two allies, of the 14 great power allies, and only one by a war involving two of the allies, and only one by a war involving one state of the allies.
For none of the last five centuries have wars generally been preceded by alliances.
Alliance-war relationship varies over time. 19th century was different from 17th and 18th centuries.
Alliances have not generally played an important part in the process leading to most wars involving great powers.
Alliance-war relationship in 20th century is quite distinct from that of in 19th century and much like that in the 16-18th centuries, alliances have generally been followed by  war, but these wars have involved states other than allies.
Differences between 19th and 20th centuries cannot be explained by either the decline of balance of power system or the higher level of polarization of 20th century alliances, but most be traced to preexisting international and domestic conditions.