A timeline of WWI, the first global conflict

It may have sparked the Great War, but the assassination of Archduke Franz Ferdinand and his wife, Sophie, was not the first attempt made by the nationalists, who eventually achieved their goal during the royal couple's tour of Bosnia. Nedeljko Čabrinović made a previous attempt with a bomb that ricocheted off the couple's vehicle, leaving Sophie injured and the archduke unscathed. Yet, on the insistence of the archduke, the tour of Sarajevo continued after the first attempt, giving Gavrilo Princip the opportunity to finish the job by killing the couple with a pistol.

Though the assassination was carried out by a small group of Serbian nationalists in the capital of Bosnia, the Austro-Hungarian Empire (which was based in Vienna) saw the murder as an act of aggression by Serbia. Though much of Europe remained outside the escalating tensions of what was known as the July Crisis, the two nations had covertly been on the verge of war for some time. Within two days of Austria-Hungary's presentation of a punitive ultimatum on July 23, 1914, all diplomatic relations between Serbia and Vienna ceased.

Given the lack of communication between the two nations, Serbia began talks with Russia—then allied with France—to stand beside them in the coming conflict. By the week's end, Russia, France, Belgium, and Great Britain had all sided with Serbia.

With the secret pledge of Kaiser Wilhelm II of Germany to align with the Austro-Hungarian Empire, thus establishing what would be known as the Central Powers, the official terms of the ultimatum were sent to Serbia. Since the terms were not meant to be met, by the end of the month, the conflict became a global one.

Named for its creator, German Field Marshal Alfred von Schlieffen, the plan had been developed in 1905 in case this very situation arose. The strategy involved consecutive invasions of France and Russia performed in a circular movement in order to surprise their enemies by attacking from the flanks. Schlieffen initially believed the plan would take less than two months to defeat the Russian forces in the eastern theater.

On Germany's western front, Schlieffen sent troops into Belgium as a part of a greater tactical movement toward France. Afterward, Britain—along with all other countries involved—tried to rally its people to unite for the cause. Britain used the justification that defending Belgium was a selfless act, though some saw these proclamations as propaganda.

France sent troops to Alsace to confront the approaching armies sent by Wilhelm and Schlieffen. Alsace was then a territory in Germany near the Belgian border, as well as a strong tactical point from which to defend France from invasion. Alsace has frequently changed hands between Germany and France.

Battles on the eastern front included a strong Austro-Hungarian invasion of Russia through Prussia and Poland. This movement preceded one of the war's deadliest battles, which took place within the first month of the war.

German armies surrounded and routed the Russians on the eastern front after learning of their plans through intercepted communications. Approximately 125,000 Russians were captured during the battle. The Germans' swift action before Russia could fully utilize its massive army—the largest in the world at the time—proved decisive.

September brought the creation of the Treaty of London, in which the Allies laid the groundwork to secretly ask for Italy's help, due to its border with Austria. Italy had previously been aligned with Austria-Hungary and was reluctant to join, waiting until spring of the following year to sign the treaty.

With tremendous resources allocated to the fight, the First Battle of the Marne saw British and French troops sent west toward the invading German forces. The mobilization effort commandeered 600 taxis to move troops to the front, located east of Paris. The Allies defeated the German forces, disrupting Schlieffen's plan.

Taking Ypres was necessary for both the Germans and the Allies as they continued north after the First Battle of the Marne in a movement known as the Race to the Sea. The fighting was close and brutal, fought from dugout trenches. Though the battle halted the German push to the east, both sides lost over 100,000 soldiers.

The British naval blockade was established to control the North Sea above Germany, which was a key area for supply routes. The blockade stemmed from the flow of all listed contraband. Food was included in the list of prohibited items, which proved to be a controversial decision, as Germany claimed 763,000 civilians died of starvation and related disease after the war. The blockade remained from 1914 to 1919 and was credited as being a pivotal action toward the Allied victory.

The Ottoman Empire had been losing ground since the First Balkan War in 1912 and was anxious to align with a major player in Europe. It eventually sided with Germany, confirming the Allied forces as enemies—British naval ships had already begun pursuing Ottoman ships in the Black Sea prior to the latter's official decision to join the war.

In Constantinople, Sheikh-ul-Islam, a religious leader of the Ottoman Empire, declared a holy war against the Allies. He encouraged his fellow Muslim followers to fight and protect Islam by protecting the empire, assuring his followers that they would be made martyrs and reach salvation if they perished in battle.

Along the western front, British and German soldiers agreed to partake in a Christmas truce. Though not officially sanctioned by leadership on either side, the truce allowed the men to meet in the area between the trenches, where they exchanged gifts, sang songs, and took pictures. Truces would occur after, though not always on holidays and were never officially sanctioned. The Christmas truce of 1914 also allowed each side time to bury its dead and tend to the wounded.

Utilizing its naval resources, Germany tried to enforce its own blockade in the North Sea. The attempt to stop supply movements between the Allied forces included threats from submarines known as U-boats, which attacked neutral supply ships headed for trade with the Allies and even sunk passenger ships filled with civilians.

During the second battle at the strategic stronghold of Ypres, Germans used chlorine gas on Allied troops. It was the first time the gas had been used as a weapon, and it would be used again two days later against Canadian soldiers fighting to hold their line, which remained intact. The gas caused major casualties on both sides.

Under guidance from British War Secretary Lord Kitchener and Gen. Ian Hamilton, an Allied force of troops from New Zealand, France, Great Britain, and Australia mobilized on the Greek island of Lemnos with the aim to launch an attack on the coast of Turkey. The battle took a heavy toll on Allied troops but established two separate beachheads.

As part of their blockade of Allies in the northern seas, the Germans made one of the war's most infamous assaults on the civilian passenger liner Lusitania. The ship had been traveling from New York City to Liverpool, England, and was secretly carrying munitions. Among the 1,198 casualties from the attack, 128 American lives were lost.

Though previously supporting Germany and Austria-Hungary in a pact dating from 1882, Italy joined the war on the side of the Allied forces on May 23, 1915. Much of the incentive for the switch lies in the Allies' offer in the Treaty of London, signed in secret by Italy in April 1915, which guaranteed the Italians control of the northern territories bordering Austria-Hungary. Other territories in the pact included port cities in Albania and portions of the Ottoman Empire.

Along with the battles at the Marne, the fighting at Verdun was some of the most brutal of the entire conflict. In the first eight hours, German forces shot over 2 million shells at French troops. The battle lasted over 300 days and cost approximately 800,000 lives.

The largest naval battle of the entire conflict, the Battle of Jutland involved 250 ships and around 100,000 men. While the attack was meant to be a German ambush on British vessels, code breakers deciphered the plan early enough to get the British fleet out to sea in time for the assault.

One of the most brutal of the war, the First Battle of the Somme was an attempt by British commanders to end a long stalemate of close combat and trench warfare against the Germans. The British and French wisely decided to take the initiative in the wake of the Germans' continuing assault on Verdun. The battle lasted five months, created over 1 million combined casualties, and earned Sir Douglas Haig the nickname "The Butcher."

Gen. Erich von Falkenhayn wanted the Battle of Verdun to end quickly and easily, and his use of extensive troop regiments and incredibly large amounts of artillery were designed to do just that. But after many months and conflicts among German senior officers, his efforts failed. Falkenhayn ended up resigning over his mistakes in strategy and misuse of troops and supplies needed elsewhere.

After the attack on the Lusitania, Germany temporarily ceased its use of unrestricted submarine warfare under pressure from the United States and other nations—but not for long. The Germans now considered any ship an enemy vessel, meaning merchant carriers and passenger ships would be attacked without notice. The decision to continue these attacks came from commanders including Wilhelm, who saw the U-boats as necessary tools to win the war.

Citing the Germans' unrestricted U-boat attacks as one of the main reasons, U.S. President Wilson cut diplomatic ties with Germany. Wilson's announcement mentioned standards of international law and implied that he might soon ask Congress for a declaration of war against Germany if the attacks continued.

President Wilson approached a joint session of the United States Congress to ask for a declaration of war against Germany on April 2, and Congress approved the measure on April 4, issuing the formal declaration two days later. Wilson cited not only the U-boat attacks but also Germany's attempts to get Mexico to align with them in order to put greater pressure on the U.S., which had maintained neutrality to that point.

Nearly two months to the day after the formal declaration, Gen. John J. Pershing arrived in France with his colleagues to begin strategizing how best to establish American forces throughout the various conflict zones. Though thousands of Americans were already volunteering to meet medical needs in the area, Pershing's presence was seen as an important symbolic moment for the Allied forces.

The first American troops numbered 14,000 and arrived in the French port city of Saint-Nazaire, a location kept secret in order to evade German U-boat attacks. British soldiers referred to the new troops as "Doughboys," as they hadn't yet experienced the brutal trench warfare known by fighters already serving on the western front.

The Battle of Cambrai included the first large-scale use of British tanks to try to surprise the German forces. A total of 476 tanks were used in the battle, though little ground was taken in the offensive, as German forces responded with heavy artillery fire to beat back the encroaching Allies.

After the leftist group the Bolsheviks took control of Russian military headquarters, the country shifted its previous priorities in order to focus on helping impoverished citizens. To that end, foreign affairs official Leon Trotsky tried to spur the Allies toward peace negotiations with the Central Powers but, hearing nothing, eventually settled for an armistice with Germany and Austria.

President Wilson's presentation of his Fourteen Points came just less than a year after the United States became involved in the global conflict. The points put forth the groundwork for a global agreement to take hold after the end of the war. The agreement included a "general association of nations," which would provide stability and protection for countries of all sizes.

Gen. John J. Pershing had the idea for a newspaper written by and for the American military forces. Stars and Stripes was sent to troops on various battlefields in an attempt to boost morale. The paper's first edition had a print run of 1,000 copies, all of which sold out quickly as it found favor with soldiers from all ranks.

Women had previously been serving the war effort by working for the Red Cross and in roles as canteen girls, but the first major recruitment of women to serve in the military came when Pershing made a call for bilingual women to work as telephone operators. Out of nearly 7,000 applicants, 200 women were employed.

The Treaty of Brest-Litovsk took a disjointed Russia even further from the war it was desperate to leave by an act of armistice, though the treaty granted the Germans a substantial claim of victory. Taking two months to finalize under the continuing threat of German and Austrian advancement into the country, it effectively ended all previous arrangements Russia had made with the Allies.

With Russia out of the picture, Germany redirected all of its forces into a last effort to destroy the British and French armies. The goal was to overwhelm them before the full force of the American industrial war machine could be brought to Europe. The German's initial attack took 16 days and succeeded—leaving 200,000 British and French soldiers dead and capturing 50 miles of ground at the front.

After a carefully orchestrated attack, the U.S. First Division took the French village of Cantigny, giving the Allies an important advantage, as the city served as a valuable lookout post. The battle lasted six days and cost over 800 American lives, but the First Division prevailed over repeated attacks by German forces.

The Second Battle of the Marne showed the true prowess of the American military, as it helped the Allies stop the advancing German forces. The battle is thought to have turned the tide and made victory an impossibility for the Germans. This was the first time Americans had fought in the European theater, and they had effectively proved themselves as a modern force of well-trained fighters.

In their first independent battle, American forces engaged in a fight to take back control of the Saint-Mihiel salient—a triangle of land between Verdun and Nancy—in September 1918. German forces had occupied the area since 1914 but had begun to remove troops just days prior to the siege. The battle lasted until Sept. 16 and resulted in a major victory for the American military.

French and American forces joined for the attack at Meuse-Argonne. French military commander Ferdinand Foch gave control of his forces to Pershing, who took a total of 37 divisions into the offensive. German forces were captured, retreated, then continued to hold their ground for another month before the assault—combined with a quickly spreading influenza epidemic—forced a final retreat.

When the Germans signed the armistice at Compiègne, it meant the end of all land, air, and sea conflicts, effectively ending the war against Germany on the western front. Though battles continued in other locations, this act marked the beginning of the end of the Great War, which had spanned years and claimed millions of lives. France's terms for the armistice included immediate demilitarization of Germany and the return of all prisoners of war.

At the start of December, Allied forces entered Rhineland, Germany, their movement part of the peace accord imposed on Germany by France. The French military remained in the territory for many years, with Germans taking this presence as motivation for renewed nationalism, which contributed to the rise of the Nazis.

Following the war's end, the victorious Allied nations gathered in Paris to discuss the conflict and its surrounding issues. Because the Russians had left the war earlier, they were not included in the talks. Germany was only given a chance to attend after the talks ended to hear the resulting decisions and punitive consequences.

Valentine's Day 1919 brought together a group called the League of Nations. The Allied nations set forth to create a document that provided ways to resolve disputes between nations in order to prevent further wars. Headquarters for the group office were in neutral Geneva, Switzerland. Though President Wilson had created this concept, America did not join the League of Nations due to conflicts between Wilson and the Republican congress.

The Treaty of Versailles, the result of the Paris Peace Conference, was signed by 32 countries. The United Kingdom, United States, France, and Italy were considered "The Big Four" directing the agreements. The treaty included punishments for Germany, including the forfeiture of land taken during the war. It also limited its military forces and put key industrial territories under the control of the League of Nations.

President Wilson was an influential designer of the peace agreement signed in Versailles in June 1919, but the United States Congress refused to ratify the treaty, marking a first for the Senate in rejecting a peace agreement. Henry Cabot Lodge, the Senate majority leader, expressed concerns that there would be a loss of power in the United States in agreeing to ratify the treaty and joining the League of Nations.

Even without an agreement from the United States, the Treaty of Versailles took effect in January 1920. Subsequently, the major players in the treaty and the largest in the League of Nations became France, the United Kingdom, and Italy. It is generally believed that the conditions of the peace agreement were a major factor in the rise of Adolf Hitler and the Nazi party, who exploited the national sense of humiliation for losing the war.

Once again, Lodge and his Republican-led Senate rejected the ratification of the Treaty of Versailles in March 1920. With a 49-35 vote to reject the peace accord, the United States left the conditions of the agreement to be enforced by European powers. Lodge was concerned not just about the United States losing control by joining with the European nations, but also about the potential cost involved in membership of the group.

The U.S. forged its own path toward the proposed peace by signing individual agreements with each nation it had battled against. The agreement with Germany gave the U.S. the same benefits that the Treaty of Versailles conferred upon its signatories, without involving membership in the League of Nations. The agreement with Austria and Hungary included similar provisions, forcing the losing side to retreat from all land acquired during the war and stop all military actions by land, air, and sea.