Final answer:
The start of the Great Depression led to the sharp rise in Nazi Party votes as it created economic hardship and political dissatisfaction in Germany, allowing the party to gain mass appeal and eventually lead to Hitler's chancellorship.
Step-by-step explanation:
The start of the Great Depression is most likely the event that accounted for the sharp increase in votes for the Nazi Party from 1928 to 1930. The Great Depression caused tremendous economic turmoil in Germany which led to high unemployment rates and widespread dissatisfaction with the current government. This environment provided fertile ground for the Nazi Party to gain mass appeal by promising economic solutions, nationalistic resurgence, and assigning blame to various groups, including Jews and the existing Weimar government. The desperation of the German population for relief from the depression allowed the Nazi Party to capture an increasingly significant portion of the electorate, culminating in Adolf Hitler's appointment as chancellor.