The British Empire fears the rise of the German army, more specifically of its navy. Britain comes out of isolation, moves closer to France, and then to Russia. Together, they form the Triple Entente. In the Balkans, the Austro-Hungarian Empire annex Bosnia and Herzegovina, much to the displeasure of neighbouring Serbia which dreamed of one day uniting the South Slav people. 

This project appeals to Russia, which diplomatically allies itself with Serbia. On June 29, 1914, a young Serbian nationalist from Bosnia murders the heir to the throne of Austria and his wife in Sarajevo. Austria-Hungary accuses Serbia of having organised the attack and despite Russian threats declares war the following month. In a few days, the conflict spreads between the countries of the Triple Entente and the Triple Alliance. Only Italy remains neutral for the moment. 

The German plan is to overcome the French army, concentrated in the East, by planning an attack from the north. To achieve this, Germany invades Luxembourg and Belgium, in violation of their neutrality in the conflicts. The French, British and Belgian armies are forced to retreat. Fearing the capture of Paris, the French government moves to Bordeaux. But the German army turns away from the city to continue surrounding the French army. They are then attacked on the flanks by the army of Paris which forces them to retreat further north, marking the failure of the Schrieffer plan. 

The new German objective is to takeover the strategic ports of Calais, Dunkirk and Boulogne to cut British supplies. The inferior Belgian army cannot resist the German advance. In the plain of Yser, the choice is then made to open lock gates to flood the polders. With the German army stopped in their tracks, the front-line is etched out with the construction of 700 km of trenches, stretching from the North Sea to Switzerland. 

With the war front-lines stabilised in the west, Germany sends its troops to the east to fight against a Russian offensive, which puts pressure on Austria-Hungary. After some hesitation, the Ottoman Empire decides to support Germany in the war. This creates several new fronts: one in the Caucasus, another in the Sinai against the British protectorate in Egypt with the goal of controlling the Suez Canal; and finally a third front in the British protectorate of Kuwait over the issue of oil resources. To weaken the Ottoman Empire, Britain supports an Arab rebellion by promising them independence in liberated lands. Finally, Italy declares war on Austria-Hungary with the hope of gaining new territory.

In Asia, Japan went to war against Germany and seized its colonies in the Pacific and China. In Africa, German colonies are stormed by French, British and Belgian forces. Many people from colonised territories are enlisted in European armies. France mobilises nearly 800,000 people, a large proportion of whom are sent to Europe. The British Empire, for its part, enlists 2.7 million men from its dominions and colonies. More than half come from British India. In the Balkans, Bulgaria goes back to war alongside the Central Empire's. 

The country has a great territorial appetite and wants to expand in all directions. Serbia is attacked on two fronts and is quickly invaded. In the West, Germany continues with military innovations. It becomes the first to organise aerial bombardments carried out by zeppelin airships. London and Paris are regularly attacked. The air force is initially used for tracking and reconnaissance, but planes are quickly fitted out with machine guns, resulting in the first aerial battles. 

In another first, Germany launches submarine wars in British territorial waters, sinking ships it encounters. Finally, in the trenches, both sides use toxic gases that cause many casualties. Despite some attempts to find breakthroughs, the front-line of war remains fixed, at great human cost. In the trenches, soldiers who survived the fighting are forced to live in harsh conditions.

Mud, vermin, rats and the smell of decaying corpses put their nerves to the test. In the spring, the French side begins mutinies that would be suppressed. Germany also tires of the stalemate. The country is now focused on war on the economic front and sends its submarines to the Atlantic to sink all kinds of ships, even commercial ones, heading to the United Kingdom. Exhausted by war, Russia suffers more than 1.7 million military casualties. 

Morale is at its lowest point on the front lines and among the public. Then takes place a short revolution that brings down the regime of the Tsars. At the same time, the United States of America finds itself becoming a victim of the commercial blockade in the Atlantic. They decide to go to war alongside the Allies. In Russia, a second revolution allows the Bolsheviks to come to power, who immediately sign a ceasefire with the Central Empire's. 

With the Russian front under control, Germany concentrates its troops on the west. The country succeeds in a breakthrough in the trenches and approaches Paris, which it bombard. But the German army moves too fast to the south. The French army counterattacks and disintegrates German defences. In panic, German soldiers retreat to the north. From this moment, the Allies lead on all fronts. 

In Germany, mutinies and a revolutionary wave forced the emperor to abdicate and allows the signing of the Armistice, marking the end of the “Great War” that kills more than 18 million people. On June 28, 1919, a peace treaty is signed at Versailles. German representatives are not invited and the country is forced to accept all demands of the Victor's. Germany and its allies are held solely responsible for war damages and must pay heavy compensation. Austria-Hungary and the Ottoman empires are dismantled, making way for new countries or colonies. 

Germany, meanwhile, finds itself humiliated and indebted. Its army is disbanded and colonies shared among the Allies. The country cedes roughly 15 percent of its territory to France, Belgium, Denmark and Poland, which is recreated. The only consolation is Germany remains largely intact due to no fighting on its territory, and its industry is still standing. The humiliation imposed upon Germany already leaves it with a desire for revenge.