Final answer:
The causes leading up to World War II include the German and Russian invasion of Poland, and the Treaty of Versailles. The Attack on Pearl Harbor was not a cause leading up to the war, but it was the reason for the United States' entry into the conflict.
Step-by-step explanation:
The events that directly led to the outbreak of World War II were numerous and complex. Among the causes were the German and Russian invasion of Poland, which marked the beginning of the war in September 1939. Additionally, the harsh terms and repercussions of the Treaty of Versailles fuelled German resentment and the rise of Adolf Hitler. The Treaty had imposed heavy sanctions on Germany and resulted in territorial losses that Germans viewed as unjust. The Nazi's subsequent violation of the treaty by rearming and expanding German territory were indicators of the forthcoming conflict.
However, the Attack on Pearl Harbor on December 7, 1941, was not a cause leading up to World War II, but rather the catalyst for the United States' entry into the war, after it had begun. Prior to the attack, the U.S. maintained isolationist policies, but the aggression by Japan eliminated any possibility of continued neutrality, and thus America joined the global conflict.
In summary, while the attack on Pearl Harbor was a pivotal event in World War II, it was not an instigating cause but a consequential response that brought the United States actively into the war.