How do alliances increase fears of war?
I would take this question and apply it to a different point in time. If we examine how alliances forged can be binding to nations and lead to war, I think that World War I would be a great example of this. Hostilities leading to the First World War can be traced to a series of alliances with nations. These alliances, both secret and direct, led to the binding of nations' foreign policy. When one nations plunged into war, it ended up pulling others into such conflict, as well. This is one such example of how alliances formed can increase the fears and realities of war. Nations lose some of their autonomy when such binding and constricting alliances are forged. In recognition of national and diplomatic word, alliances can help to decrease national self- determination. In this light, one can argue that if alliances are not carefully sought and deliberately cultivated, there exists a very real propensity for war.
According to international relations scholars, alliances make other countries afraid and can (under certain conditions) make war more likely. You could argue that this happened, for example, in WWI.
Countries tend to enter into alliances to keep themselves safe. However, when they do this, they make other countries afraid. For example, imagine if Country A and B are low-level enemies. They aren't about to go to war, but they are suspicious of one another. So now A enters an alliance with Country C. What will country B think? They will worry that A and C will team up and attack them. They may want to attack first to try to start and win a war before A and C are ready.
In WWI, alliances between France and Russia (among others) made Germany worried. This is one reason that they acted so aggressively at the start of this war.