At the start of the war, Britain and France had developed into superpowers with vast colonial empires,
but their colonies were slowly starting to assert themselves, striving for independence.
Several other rising powers, especially Germany, Italy and Japan, envied them and desired the same power.
The traditional large land-based empires like Austria-Hungary and Russia were unstable because of ethnic and nationalistic stirrings among their multi-ethnic populations.
Since the Napoleontic Wars,
this volatile mix of heavily armed states had been held in check by the Congress of Vienna, which had set up a balance of powers.
However technological, economical and social developments during the Second Industrial Revolution had, despite several re-alignments, distorted that balance.
Militarism was dominant in several states, especially Germany and Russia.
Several countries were engaged in a naval arms race; in the 35 years before the war military spending in Europe rose by 320%, in the last 5 years by 50%.
Worse, military doctrine throughout Europe was based on the Prussian tactics of the Austro-Prussian War of 1866 CE
and the Franco-Prussian War of 1870 CE,
where Prussia had won by mobilizing quicker than its opponents and using railways to rapidly transport troops to the front.
This ensured that though almost all parties involved fought to defend their interests and in the early 20th century CE the strategic advantage lay in defense too, the war was fought offensively.
The tinderbox was sparked when Serbian nationalists assassinated crown prince Franz Ferdinand of Austria-Hungary.
The resulting conflict could have remained limited to the Balkans, but Austria-Hungary did not dare to act against Serbia alone and requested backup from Germany, which in turn aggravated Russia.
When Russia mobilized its troops, inter-state diplomacy failed miserably and in a cascade all major powers set their pre-war made plans in motion.
Once started, these plans could not be changed without wrecking the overall strategy of each country, turning them into juggernauts.
All countries mobilized their armies as fast as they could.
Declarations of war flew around and within a few weeks the Great War started.
Initially Germany and Austria-Hungary, both members of the Triple Alliance, faced off against the Triple Entente, made up of France, Britain and Russia, forcibly joined by Serbia and Belgium.
Every country hoped and ignorantly believed that the war would be short.
The German strategy was to slice through neutral Belgium and northern France in a sickle-maneuver, a plan concocted by strategist von Schlieffen;
defeat France before Russia could reach them and afterwards fight Russia in the east.
The Germans encountered a Belgian army that was outdated in organization and equipment, but also had strong forts, which were modern.
Only by a combination of aggressiveness, luck and ultra-heavy howitzers did they manage to break through.
French counteroffensives in Lorraine and at the Sambre failed and they were forced to retreat, pulling the British expeditionary force on their left flank with them.
However the German Schlieffen-plan, already faulty, was executed badly by chief of staff von Moltke and failed too.
The Germans retreated some distance and then both sides dug in in northern France and Belgium.
The center of the fighting briefly moved northwest, yet there too both sides were equally matched and after great losses they entrenched themselves also.
In the east warfare was much more fluid.
The Russian army aimed at Germany was forced to split itself in two wings, separated by the Masurian lakes.
The Germans halted one and defeated the other at the only 'kettle' battle of the war at Allenstein / Tannenberg.
A year later the Russians were driven out of Poland and the southern Baltic states, though in 1916 CE their general Brusilov briefly struck back.
Meanwhile the Austrians failed to conquer the small but fierce Serbia and after many large battles against the Russians were driven back to the Carpatian mountains.
Thereafter they became something of an auxiliary force, while the Germans carried the bulk of the fighting against the Russians.
In 1915 CE, Germany and Austria-Hungary together and helped by Bulgaria, conquered Serbia, though combat in the Balkans continued until the end of the war.
There also was a lot of fighting on the borders of the Ottoman empire, which lost ground to Russia, Britain and Arabs.
On the whole the Great War was not a single one, but an amalgamation of several.
Because some of the countries involved in the fighting had colonies, it soon became global.
Germany lost many of its overseas colonies early in the war,
though a small force under von Lettow-Bulock held out in east Africa until the end of the conflict.
During the course of the war many more countries joined in:
several British Commonwealth countries, Montenegro, Japan and the Ottoman empire in 1914 CE;
Italy and Bulgaria in 1915 CE; Romania and Portugal in 1916 CE; USA, Greece and Brazil in 1917 CE.
Some, like Japan, had limited strategic objectives and fared well; others, like Italy and Romania, were opportunistic and suffered heavily.
In Europe, by 1915 CE two frontlines had been established, both lines of trenches and fortifications stretching 750 kilometers in the west and 1250 in the east.
While in the east the opponents were on average 3 - 4 kilometers apart, in the west the distance was 200 - 300 meters, sometimes as little as 25.
The Germans had chosen their positions well, on high ground.
They reversed their original strategy, settled for defense in the west and transferred as many troops as possible to the eastern front.
The French needed to liberate their lost provinces, where much of their mineral resources and industry were located.
Their army, and the British one also, had been strengthened by many new recruits.
The western generals launched several offensives that all gained little ground or none at all, at high cost in lives.
Infantry on foot, hampered by sluggish communication with headquarters kilometers behind the frontlines,
was unable to attack fast enough to be able to break through the defensive lines anywhere, which were often kilometers deep.
Artillery, firing indirectly, was not yet accurate and responsive enough to coordinate its attacks with the infantry.
Barbed wire, trenches and bunkers slowed the soldiers; machineguns and rifles killed them.
The Germans especially handled these tools well, throughout the war evolving their methods from trenches via defense in depth to elastic defense.
During the war new weapons like submachine guns, tracer bullets, flamethrowers, poison gas,
airplanes and especially tanks
were used to make offensives feasible again, but none proved decisive.
While the land armies were mostly locked in a stalemate, at sea the navies had used the decades before the war to modernize their fleets.
Gone were the sailing ships of the previous century; battleships now ruled the waters.
The Royal Navy locked the German fleet up in the North Sea and the Baltic, strangling German supply lines.
The German fleet tried to break out several times, on the whole with little success.
The largest naval battle was the indecisive Battle of Jutland in 1916 CE.
U-boats were more effective for the Germans, until the adoption of the convoy system by the allies in 1917 CE.
At times the submarines waged unrestricted attacks on merchant ships, which eventually brought the USA into the war.
In 1916 CE the allies had conscripted many troops
and their war industries had increased their output vastly, so they were again confident of success,
but the Germans did not remain idle either.
On the western front two enormous battles were fought, a German offensive at Verdun and an allied one at the Somme.
Both gained little ground and cost hundreds of thousands of lives.
Failing offensives continued into 1917 CE, however war-wariness set in on all sides.
French soldiers, fed up with the massive death-toll, went on strike in the 'Mutiny of 1917';
civilians in Germany and Austria-Hungary were starting to suffer from food shortages.
More important was the collapse of the Russian economy and the subsequent bolshevist revolution.
The country, divided and in turmoil, could offer no resistance to the German armies, which easily overran a huge part of it.
Russia was plunged into a civil war that lasted four years, in which many foreign powers meddled.
The collapse of the eastern front allowed Germany to transfer 50 divisions to the west.
With an advantage of 197 good divisions against 178 weary ones, but less guns, tanks and airplanes, they launched a final offensive in 1918 CE,
hoping to win the war before the Americans could arrive in large numbers.
The offensive was made up of several successive attacks, each gaining some ground because of the new German stormtrooper tactics.
Yet each failed to achieve a decisive breakthrough, like before, though it was a close call.
The Spanish flu arrived, killing more people than the guns had done in four years and hitting the underfed Germans the hardest.
Counter-offensives by the allies, including the yet indefatigable Americans, suddenly rapidly turned the tables and drove the Germans back to the Hindenburg line.
Bulgaria, Turkey and then Austria-Hungary dropped out of the war.
The German emperor was forced to abdicate and Germany surrendered to a set of harsh peace terms.
In Europe, the Great War had no winners, only losers.
Globally, around 10 million soldiers and 7 million civilians died, 20 million were wounded and 7 million went missing.
Some countries lost 10% - 15% of their adult male population.
Of the main players, Turkey and Austria-Hungary were broken up; Russia plunged into a civil war; Germany burdened by a heavy repatriation yoke; Britain and France completely worn out.
Other states too had lost lives and/or territory.
The maps of eastern Europe and the Middle East were completely redrawn; many new states arose.
Yet the underlying problems that had caused the war were not resolved.
They simmered, then boiled into nationalism and fascism and within a generation plunged the world into a new conflict, World War II.
On the military level, World War I marked the transition to modern warfare.
At the start of the war several old fashioned generals pitted muscle and bravery against recently developed innovations in gunnery,
failing to realize that technology was becoming as important as soldiers.
Rifles, machine guns and long range artillery delivering indirect fire caused heavy casualties.
But at the end of the war several innovations had emerged that focused on mobility instead:
predicted and suppressive artillery fire; stormtroopers; motorized troops; tanks; airplaines; long-range communication via radio.
These came in full power in the years after the Great War and of course in World War II.
War Matrix - World War I
World Wars 1914 CE - 1945 CE, Wars and campaigns