Final answer:
World War I was a significant global conflict marked by the assassination of Archduke Franz Ferdinand, trench warfare, and the introduction of new military technology. The U.S. entry into the war contributed decisively to the Allied victory. The war's end reshaped the world's political landscape, leading to revolutions and setting the stage for a second global conflict.
Step-by-step explanation:
World War I, which spanned from 1914 to 1918, was a pivotal global conflict that drastically altered the course of the 20th century. The war involved most of the world's great powers, divided into two opposing alliances: the Allies and the Central Powers. The assassination of Archduke Franz Ferdinand of Austria-Hungary on June 28, 1914, by a Serbian nationalist set off a chain reaction among the European powers, leading to the declaration of war by major nations and marking the start of the war.
The early months of the conflict were characterized by rapid movements of troops, with the Western Front stabilizing into a grueling stalemate of trench warfare. Known as the 'race to the sea,' both sides desperately tried to outflank one another, leading to the establishment of a continuous trench line stretching from the North Sea to the Swiss border. The first fully-industrialized war, it featured advancements in military technology such as machine guns, artillery, tanks, and chemical weapons.
The entry of the United States into the war in 1917 was a significant turning point. American troops provided fresh forces for the exhausted Allies on the Western Front. By the end of the war, America's participation proved to be decisive, contributing to the eventual defeat of the Central Powers.
The war had widespread implications, including political upheaval, economic strain, and social change. The conflict facilitated the rise of socialist ideas, particularly in Russia, leading to the Bolshevik Revolution and the end of tsarist rule. Worldwide, it set the stage for various nationalist movements and revolutions, and ultimately paved the way for World War II due to the harsh peace terms imposed on Germany and other defeated nations.