Hell, by George Leroux, depicts the horrific images he witnessed at the western front.

The war quickly became a defensive one. Armies dug trenches into the earth and set up machine gun nests and barbed wire, waiting for the enemy to make a heroic but futile charge across a no-man's-land, the strip of earth that separated the trenches.

The insane object of trench warfare was to send troops “over the top” of the trenches, across no-man’s-land, and into the enemy trench. The attacking side often pummeled the enemy with artillery shells and then gave the order to attack. Machine guns cut down soldiers by the thousands.

British troops approach the Somme front where they would soon suffer the heaviest losses in British history.

Those who were fortunate enough to make it across no-man’s-land had to jump into the enemy trench and kill as many opponents as possible with the bayonets attached to the end of their rifles. Even if an attack was successful, the defending side often retreated to another trench, and a new no-man’s-land was created. All the resulting casualties might yield a net gain of fifty or so yards of territory.

WWI saw an deadly mixture of the old and the new. New weapons were used — the airplane, poison gas, the flamethrower, and massive artillery guns. But one also saw the retention of cavalry units and old military values.

The French, for instance, refused to follow the lead of British and German military forces by changing their uniforms to khaki or gray to make troops less conspicuous on the battlefield, maintaining their traditional uniform of blue coats, red hats, and red trousers that had been first used in 1830. A Paris newspaper reported that to banish the red trousers was "contrary to French taste and military function." The final decision came from the French Minister for War, whose answer was: "Eliminate the red trousers…never." "Le pantalon rouge, c'est la France," he said — "The red pants, it is France."

German and French casualties in the first months of the war were massive. By the end of December 1914, both countries had lost nearly a million men, about 300,000 killed and 600,000 wounded or missing in action. In one two-week period, the French lost nearly 300,000 men. The casualty rates were so high that by the end of 1914 most of the army regulars had been replaced by volunteers. On the eastern front, Russians suffered 2.5 million casualties in 1915.

The machine gun and bombs did their share of the damage. German "Big Bertha" guns lobbed huge artillery shells onto enemy positions. Then there was mustard gas. The Germans first used gas in 1915 at Ypres, Belgium.

But frostbite, trench foot, rheumatism, and pneumonia did incredible damage as well. In between offensive charges, there was boredom. Winter in Europe meant surviving cold, damp conditions. Soldiers also had to deal with rain, rats, lice, fleas, and the constant stench of the dead. While men were falling, women, especially from Britain, served on the sidelines as nurses, doctors, mechanics, and ambulance drivers, participating to a much greater extent than in previous wars.

Well aware of the heavy use of chlorine, mustard, and other gases, British machine gunners wore gas masks for protection at the Battle of Somme in 1916.

Such horrendous battle conditions also bred fraternization between enemies. Army officers discouraged such interplay, but it was hard to suppress given the boredom and travails of trench life. Many of the trench units lay within earshot of their enemies. Banter and songs were traded back, especially during December 1914 when Christmas approached. Germans held up a sign for their British enemies: "When are you Englishmen going home and let us have peace?" Enemy troops even played soccer with each other during declared breaks in the fighting.

Christmas 1914 saw the high point of these friendly relations between soldiers, many who lacked a thorough understanding of why they were there. Starting Christmas Eve, soldiers traded songs and food. In one case, a British soldier took a cake to a German camp and returned with a bottle of wine. On Christmas morning, troops met in no-man's land to talk, exchange gifts, or hold burial services. A German barber gave haircuts to British troops. German cigars and British bully beef were the popular barter items. "The Lord's Prayer" was recited in English and then in German at one service.

Enemies became enemies again as the war dragged on. Some of the worst fighting took place in 1916. At Verdun, Germans suffered 281,000 casualties attacking French forts; the French suffered 315,000. At the battle of Somme River, the British lost 420,000 men to death and injury, while the French lost 450,000 and the Germans lost 200,000. The numbers were staggering. In the entire Vietnam War, the United States suffered 59,000 battle deaths. Britain France and Germany lost many times this number in one battle offensive. "I am staring at a sunlit picture of Hell," wrote British poet Siegfried Sassoon to describe the carnage.

Discipline in the trenches became hard to maintain, as some soldiers turned to killing their own officers in protest of the conditions. Some French troops mutinied in 1917. Few soldiers could make sense of the continuing conflict.