Abstract
Political philosopher Niccolò Machiavelli wrote some observations on alliances, particularly their problems.
Alliances
Machiavelli, for example in The Prince, chapter 21, observed that political alliances of varying types were fraught with problems.
As a rule of thumb, a stronger partner will use you, mercenaries will sell you out, militants will take you over, and weaker partners can drag you into needless conflict.
Military alliances do not prevent wars: they may accelerate the march to war, extend war's theatres, increase war's damages, prolong the war, and sometimes give the most vindictive allies the final say in the following peace (piling up new problems). Allies may end up becoming subjects of empire run by a power they once considered a partner (as in the Athenian Empire which grew out of the Delian League).
In war, or other kinds of conflict, it is not only the result (which can sometimes be ambiguous or contested) but the whole conduct of the conflict that can vary the outcomes on alliances. Allies are often written out of nationalistic histories, or downplayed, or even turned into villains.
Common Causes
However, common causes are different, and may not even need formal alliances. Although just because you have a common cause doesn't mean that you will fight side by side. When the Persian Empire began invading Greece, the Greek cities had common cause to resist, but only a relatively few city states committed to armed resistance.
It is likely that states will find common causes with most enemies too, which is generally how wars end without total annihilation.
