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Heir to the Austro-Hungarian throne is assassinated in Sarajevo, igniting tensions across Europe.
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This declaration triggers a chain of alliances and declarations of war.
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Germany declares war on Russia (August 1) and France (August 3). Britain declares war on Germany on August 4 after Germany invades Belgium.
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Allied forces halt the German advance into France, leading to a stalemate and the beginning of trench warfare on the Western Front.
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Germany uses poison gas (chlorine) for the first time on a large scale, marking the beginning of chemical warfare.
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One of the longest and costliest battles of the war, with massive casualties on both sides.
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British and French forces launch an offensive against Germany; notable for the high casualties and the first use of tanks by the British.
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The U.S. declares war on Germany following unrestricted submarine warfare and the Zimmermann Telegram.
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Known for the horrendous mud and high casualty rates, marking little strategic gain for the Allies.
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Germany launches a series of major attacks on the Western Front, initially making gains but ultimately failing.
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Allied forces counterattack successfully, marking the beginning of the German retreat.
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An armistice is signed in Compiègne, France, ending fighting on the Western Front at 11:00 a.m. This day is commemorated as Armistice Day or Remembrance Day.
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The main peace treaty that officially ends the state of war between Germany and the Allied Powers, placing heavy reparations and territorial losses on Germany.
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The treaty marked the official end of the First World War for Austria and for the majority of the states and kingdoms comprising the former Austro-Hungarian Empire, with the exception of Hungary, who would sign their own peace treaty, the Treaty of Trianon, on 4 June 1920.
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Bulgaria had to cede the rich wheat‐growing area of southern Dobrudja to Romania and western Thrace to Greece, thus losing direct access to the Mediterranean.