Why?

In four short years, from 1914 to 1918, over 10 million men and women serving in armed forces on fronts around the world were killed, while double that number were wounded, disabled and disfigured; and at least another 7 million civilians lost their lives as well. Most died horrific deaths. But as time passes by we tend to forget, a century later, how many sacrifices were made day after day on both sides of one the most deadly conflicts in human history. Civilized Productions has produced a wonderful choral album, Sacrifice and Solace, which features an octet called the Toronto Valour Ensemble who sang these carefully selected and uniquely composed songs from that era. It is available on CD Baby. The simple translation of the Arabic word "jihad" is struggle.

The Struggle in The Trenches

Stalemate is a term most commonly used in the game of chess when the two opposing players cannot move their remaining pieces in order to win. They have reached a point in their game where new moves are futile and there is no further point to continue. As an admittedly unwinnable game, it is typically agreed to play on is simply a waste of time, energy and effort. Pride might and occasionally does intervene and, if one or both players are quite stubborn, the game could drag on ad infinitum.
At the outset of the First World War, in accordance with their Schlieffen Plan, the German armies in August 1914 had been deployed and advanced quickly through Belgium and were heading southward toward Paris while French and British troops withdrew from their positions and retreated. They stopped and fought each other decisively at the Marne river and, after a series of battles, the Germans, exhausted after marching and with their armies attacking France along the German border effectively repulsed, decided to defend the counter-offensive at the Aisne river. 
The use of heavy artillery had enabled the Germans to capture the fortified cities of Liege and Namur, and although the Belgian army successfully slowed their planned advance toward the critical port of Antwerp (encircled by four dozen defending forts), in early October it too was surrendered .  The Belgians fell back to the Yser Canal and opened sluices at high tide to flood fields and stop the German advance. Generals, however, on both sides realized there was a line from Paris northward to the Belgian coast left exposed, vulnerable to their still-mobile armies' attacks.
Within months, armies opposed each other along a line extending from Switzerland, through northeastern France and Belgium, to the coast. A "race to the sea" had ensued in September, whereby in the North the Germans were forced to retreat to a nearby ridge at Chemin des Dames and with the advantage of height, and having dug in, had stopped the British, who then also dug in and stopped a counter-attack by the Germans. These were the first entrenched soldiers of WWI. 
Noting their success, armies across the Front were hastily digging their own trenches and awaited fresh supplies. Obviously, the Schlieffen Plan had failed for several reasons, such as marching armies outpacing supply trains, yet French leaders were now intent of removing German soldiers from French soil and decided the Belgian city of Ypres would be the gateway through which they liberate not only their own country but Belgium as well. 
Fatefully, the new Chief of Staff for the German Amy, wanting to capture the ports of Dunkirk, Calais and Boulogne, had amassed an army to do so, and launched a major offensive on October 20. At Ypres, British troops held the front of the town, and French troops held its flanks. Under withering fire, disastrous for German troops, the attack was stalled, and here a young Adolf Hitler received his Iron Cross. Knowing British troops were depleted, the Germans renewed their attack, but with the arrival of forces from India, the first Territorial battalions to cross the Channel, by late-November the Germans could not break through and the First Ypres was concluded.
Kaiser Wilhelm II, who had visited his troops adjacent Ypres on October 31, was subsequently informed that a strategic quick victory on the Western Front had been thwarted - and the German high command then issued orders for a strong defensive line, consisting of protective field fortifications, to be constructed. Of the original British troops that had consisted their Expeditionary Force landing in France in August, 90% had been killed or wounded, mainly at Ypres. By contrast, the French, at the end of 1914, would suffer 300,000 casualties, and the Germans 240,000. 
The fighting at Ypres would continue for the remainder of the war, and with the Allies' plan to send the Germans home in 1914 equally quashed, troops settled in where fighting had come to a halt and were reinforced. The French had attacked at Champagne and Artois in December, but both sides conceded the war would not be over by Christmas. Meanwhile, given dwindling reserves, planners crafted not only defensive plans for the new trench war upon them, but also offensive plans to subdue and vanquish the enemy. 
The Germans had about 10,000 machine guns to support their invading army, but they were heavy and required a crew to transport and fire effectively while on the offensive. However, in a defensive scenario, they would prove incredibly effective in slaughtering counter-attacking soldiers, especially the British army's 'shock and awe' tactic of the bayonet charge. Given their rapid rate of fire, they over-heated, requiring new water and air-based systems to eventually cool them.
Bigger and more effective weapons were deployed to support soldiers and augment artillery, including the use of barbed wire. An enlisted soldier carried into battle three weapons: a rifle, bayonet and several grenades; an officer would be issued (and lead a charge with) a pistol. At the outset, the typical British battalion had two machine guns, to the Germans six. With machines guns effectively rendering the bayonet obsolete, and a terrifying death with "a quick twist to the left", they were soon made more beneficial in the soldiers' efforts to open tinned food.
Other innovation occurred in the trenches; soldiers required in small units to cross lines, to scout and capture enemy soldiers at night-time, developed their own lethal weapons, such as clubs, by improvising entrenching tools. Barbed wire had been invented in America and introduced at the time of the Civil War to enclose cattle, and was found to effectively stop infantry advances, whereby stranded troops could be massacred. Throughout the war, at great peril, soldiers were constantly repairing their own wire or cutting enemy wire in the hopes of holding and gaining ground.
On Christmas Day, as a reflection on truly war-weary soldiers, rather extraordinarily, a series of ceasefires occurred spontaneously along the Western Front. Known as The Christmas Truce, carols were sung and gifts exchanged in No Man's Land between them, commonly called Death Traps and where killed soldiers still lay, unburied. Troops would stay entrenched along a line of approximately 440 miles - The Western Front - for four years while artillery technology continued unabated. In fact, during the Great War, artillery guns caused more deaths than any other weapon.  
Behind the initial line of trenches, in "the rear", were command posts and field hospitals, as well as numerous artillery positions consisting guns of varying sizes, able to send their projectiles miles across lines. By 1917, in addition to the appearance of unwieldy poison gas and cumbersome tanks on European battlefields, planes flew reconnaissance missions and fought overhead, and balloons lifted brave spotters into the air, while miners dug labyrinths underground to move men and material unseen, as well as plant huge caches of explosives directly beneath enemy positions.
"The war will be ended by the exhaustion of nations rather than the victories of armies," observed Winston Churchill. Yet generals continued to attempt to exhaust their enemy, whether by exhausting their supply of resources or manpower.  The trenches became elaborate systems, built to defend in a zig-zag or dog-leg manner, and from which to launch attacks, by sending men "over the top". Soldiers were rotated, due to the admitted horrors of life on the frontline, pulled back after a week to the support line, then to the reserve line and finally to the rear, before heading back to the front.
In this environment, on both sides, as the war progressed artillery was thought to be the best option to break the stalemate and in early 1915 massive barrages began to level defensive structures and eliminate barbed wire along the front. To maximize its effectiveness, artillery fire became very controlled and monitored. It was the Allies who introduced the creeping barrage whereby advancing troops would methodically follow a moving wall of falling shells - however, sadly, enemy artillery proved equally as effective in stopping these advances. 
Eager to defeat the Allies before the United States could make a meaningful impact in the war, the Germans organized and executed their Michael offensive in 1918. After an initial breakthrough, the Allies had pushed the Germans back across conquered territory - including the vaunted Hindenburg Line. But, now that the war had emerged from the trenches, and with their soldiers once again exposed, the final year would prove as deadly as the first for combatants.
In a stalemate for nearly four years, the war of attrition had run its course, and with Germany finally exhausted, its military leaders decided to abandon the war. The importance of trench warfare, and all that was required to sustain it, clearly played a major role in the eventual outcome of the conflict, which with the signing of the Treaty of Versailles would see a rise to power of Hitler and his national socialists, and the outbreak once again of another World War two decades later in 1939.