Final answer:
Bismarck's fear from the Bulgarian Crisis stemmed from the potential for a regional Balkan conflict to drag in the major European powers due to the dense network of alliances, threatening the continental balance of power and potentially leading to a widespread war.
Step-by-step explanation:
Bismarck feared that the Bulgarian Crisis could spark a larger European conflict because of the complex system of alliances that existed at the time. The crisis intensified his fear due to the deepening alliance between the Serbs, Bulgarians, and Russians, which threatened to challenge Austria-Hungary's influence in the Balkans and upset the balance of power. Moreover, Bismarck was concerned about the volatility within the continent, where imperial rivalries and historic grievances made the diplomatic situation tense and fragile. With Prussia's acquisition of Alsace-Lorraine after defeating France, a militarized border had formed, and the intricate alliance networks further increased the likelihood of a regional conflict escalating into a general war. Ultimately, Bismarck correctly anticipated that the escalation of a regional conflict in the Balkans could draw in the great powers of Europe into a catastrophic war.