Final answer:
The assassination of Archduke Franz Ferdinand of Austria-Hungary on June 28, 1914, started World War I. The Treaty of Versailles, signed in 1919, demanded Germany to accept full responsibility for the war and imposed severe penalties, contributing to the rise of Hitler and setting the stage for World War II.
Step-by-step explanation:
The incident that began World War I was the assassination of Archduke Franz Ferdinand of Austria-Hungary on June 28, 1914. This event triggered a series of alliances and declarations of war that embroiled most of Europe into a conflict of unforeseen scale and devastation. The first few months of the war saw a swift mobilization of troops and a series of quick strikes that the European powers had hoped would lead to a short conflict. However, this rapidly transitioned into a deadlock with trench warfare that led to extensive casualties on both sides.
The Treaty of Versailles was signed on June 28, 1919, and had severe ramifications for Germany, forcing them to accept full responsibility for the conflict under the "war guilt clause". This, coupled with territorial losses, military restrictions, and heavy reparations, contributed to political instability and economic hardship. These punitive measures and sentiments of humiliation and injustice directly contributed to the conditions allowing the rise of Adolf Hitler and the outbreak of World War II. Although the treaty aimed to prevent future wars, it instead created resentment and paved the way for future conflicts. Thus, while the Treaty of Versailles officially ended World War I, it planted the seeds for the international tensions that would eventually lead to World War II.