The Assassination of Archduke Ferdinand in Sarjevo on June 28, 1914 began World War I when a bomb and later a shot was used to kill him.

Germany continued its invasion of Europe and when it crossed Poland, Great Britain and France were obligated via treaty to declare war on Germany.

Whoa hold on let's reevaluate this. The bombing of Pearl Harbor did not trigger WWII. On September 3, 1939, France and Britain declared war on Germany following Germany's invasion of Poland. This is a generally accepted date for the start of WWII, but some historians argue different dates (for our purposes, it doesn't really matter). The good ol' US of A didn't declare war until after the surprise bombing of Pearl Harbor by the Japanese on December 7, 1941. So no, Pearl Harbor didn't start WWII. The war had been going strong in Europe for two years prior to that.

WWI was triggered by the assasination of Archduke Ferdinand, however, the tension among the European nations were at all time high at the time. A combination of nationalism, imperialism, militarism and most importantly alliance systems led to the outbreak of the First World War. As for WWII, the treaty of Versailes from WWI contributed greatly to the conflicts of WWII.

I: Assassination of Archduke Ferdinand
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II: Bombing of Pearl Harbor
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Come one people, can't this be googled? Stop trying to boost your score and waste our time.

I apologize, aequitas. You're correct; my mind automatically jumped to the US involvement in WWII. Didn't even think past that when typing.

Again, my apologies. 5*s for you.