World War I, also called First World War or Great War, an international conflict that in 1914–18 embroiled most of the nations of Europe along with Russia, the United States, the Middle East, and other regions.
The war pitted the Central Powers—mainly Germany, Austria-Hungary, and Turkey—against the Allies—mainly France, Great Britain, Russia, Italy, Japan, and, from 1917, the United States. The war was virtually unprecedented in the slaughter, carnage, and destruction it caused.
The next day Germany sent troops into Luxembourg and demanded from Great Britain, which had no concern with Serbia and no express obligation to fight either for Russia or for France but was expressly committed to defend Belgium, on August 4 declared war against Germany.
Italy had confirmed the Triple Alliance on December 7, 1912, but could now propound formal arguments for disregarding it: first, Italy was not obliged to support its allies in a war of aggression; second, the original treaty of 1882 had stated expressly that the alliance was not against England.
On July 31 Germany sent a 24-hour ultimatum requiring Russia to halt its mobilization and an 18-hour ultimatum requiring Both Russia and France predictably ignored these demands.
On August 1 Germany ordered general mobilization and declared war against Russia, and France likewise ordered general mobilization.World War I combat was a clash between 19th-century tactics and 20th-century technology.Imagine an American Civil War battle with large groups of men charging across open ground except the other side has heavy artillery and machine guns.Our editors will review what you’ve submitted and determine whether to revise the article.Join Britannica's Publishing Partner Program and our community of experts to gain a global audience for your work!Nations from across all non-polar continents were involved, although Russia, Britain, France, Germany, and Austria-Hungary dominated.Much of the war was characterized by stagnant trench warfare and massive loss of life in failed attacks; over eight million people were killed in battle.Leopold, Graf von Berchtold, saw the crime as the occasion for measures to humiliate Serbia and so to enhance Austria-Hungary’s prestige in the Balkans.Conrad had already (October 1913) been assured by Germany’s support if Austria-Hungary should start a preventive war against Serbia.But, meanwhile, the German Foreign Office had been giving such encouragement to Berchtold that already on July 27 he had persuaded Franz Joseph to authorize war against Serbia.War was in fact declared on July 28, and Austro-Hungarian artillery began to bombard Belgrade the next day.