How was World War I largely responsible for World War II?
The reasons for any war are complex and can be difficult to tease apart, but there is ample evidence that the "ending" of World War I led to World War II for many reasons. I do not know, of course, which particular factors your studies have focused on, but I can think of three that you are likely to have learned about.
First, Germany had to pay to the Western nations, the Allies, as a condition of peace, an incredible sum in reparations. This caused a great deal of resentment among the Germans, since it harmed the economy for everyone, and this resentment was harbored and passed down to the next generation. The economic harm caused also led to the rise of Hitler, who capitalized on the economic problems and used them as a kind of political slate to be elected.
Second, Germany was forced to disarm as a condition of peace, limited to a tiny army and a few warships. Naturally, this disarmament had caused great resentment, which ultimately motivated the Germans to develop the weapons and machinery with which it fought World War II. Unlike today, I believe there was not much provision for inspection to make sure Germany was complying, so rearmament was done quietly, without attracting a great deal of attention for a while. Had the German military not been quashed so greatly or had the Allies paid a bit more attention, Germany might not have created such a great war machine.
Third, a great deal of land was taken away from Germany as a condition of peace, causing a further resentment that held sway throughout the years following World War I, leading to German action to regain that lost territory.
In summary, the "peace" that ended World War I was so repressive to Germany that the smoldering embers of resentment finally burst out into World War II. I remember my father, who fought in World War II and liberated concentration camps, saying that if the Allies hadn't been so bent on rubbing the Germans' noses into it, we might have never had another war.