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 for Hearts and Minds

When the heir to the Austro-Hungarian throne was shot and killed in Sarajevo in the summer of 1914, igniting a powderkeg that sent shockwaves around the world, industrialized nations across Europe were suddenly galvanized and armies mobilized within days. Led by competitive and idealistic monarchs, leaders among these empires were equally determined to maintain their control of natural and human resources to fuel factories and expand markets globally.
In addition to cars and trucks replacing horses and buggies, there were many other quiet changes occurring at the outset of the twentieth century impacting an ever-growing disposable income afforded the legions of new factories workers and administrators. Soon enough, watches strapped to wrists, popular among officers of the British Army - convenient and critical for timely coordination of efforts on the battlefield - replaced pocket watches.
With horses no longer polluting city streets, and human refuse being swept away into sewage systems, urban planners began to incorporate open spaces for the benefit of citizens, from sidewalks to parklands, while others recognizing people had both time and money on and in their hands began planning to acquire their wealth; publishers of newspapers, magazines and books flourished, and, with the advent of moving pictures, soon enough people were flocking to cinemas.
People were happy to spend their money. Assembly lines and mass production led to mass marketing. When Ford introduced their Model T in 1908, individual tastes and preferences were irrelevant, as each buyer had the option of simply purchasing a vehicle painted black. The way nations did business was changed forever with the introduction of national advertising, department stores and mail-order, as well as advertising agencies, public relations and brands.
In order to reach consumers and influences purchase decisions, leaders of ad agencies relied not only on newspapers but also posters and billboards, and direct distribution of handbills. In America, for example, a range of new products were competitively promoted to consumers from Levi Strauss's denim pants and King Gillette's disposable razor to cameras, chewing gum, bicycles, telephones, electric lighting, numerous household appliances and barbed wire.
Capitalism was enjoying its infancy, though balanced by democratic notions of freedom and liberty for all, including safety and security. Convenience and comfort were certainly available to those who could afford these now-common luxuries. After all, the majority of these burgeoning populations required warm homes, safe streets, schools and jobs for their children. An educated and mobile workforce enabled growth on many levels and, admittedly, times were good.
Until, on June 28, 1914, a young Serb leapt from his cafe seat and seized the opportunity to kill Franz Ferdinand and his wife Sophie, which he did with lethal efficiency using only two bullets. Five years later, with the signing of the Treaty of Versailles, a global conflict was officially ended, having effectively caused over 36 million human casualties - 16 million dead and 20 million wounded. During the war, 6 million people alone had died from either disease or starvation.
Military deaths on the battlefield were no longer due to the typical loss of blood from a bullet or several, a stab wound or several, or caused by the shocking effects of a nearby explosion or losing a limb to a passing cannon ball, infection or drowning at sea. In the Great War, soldiers might be blown to mist, crushed by a tank, suffocated by poison gas, burned alive by a flamethrower, suffer a heart attack while falling from a plane, or cut in half by rapid firing machine guns.
One hundred and one years ago, with declarations of war formalizing battle lines and intentions of empires cementing the fate of their people, Britain had a relatively small army compared to the continental armies swiftly mobilized and deployed across Europe. The mobilization of an army was tantamount to a declaration of war, and Britain in 1914 was the only Great Power to not have conscription, unlike France, Russia, Germany, Italy and Austria-Hungary.
In addition to soldiers, horses were mobilized. The British had 165,000 horses prepared for cavalry duty, the Austrians 600,000, the Germans 715,000, and the Russians over a million. Expected to fight alongside the British, when Britain entered the war on August 4 - defending Belgium's right to neutrality - so too did Canada, Australia, New Zealand, India and South Africa. Britain sought hundreds of thousands of new soldiers, and the appeal was met with an enthusiastic response. 
The recruitment of volunteers involved the design and distribution of posters on one hand to foster nationalistic patriotism, expecting men to respond to a need, to proudly fight an imposing enemy, to maintain the honour and glory of The British Empire, and on the other to learn a new trade or skill, to become better artisans and craftsmen while serving King and Country, ensuring a worthwhile job at home after returning from the front.
In 1914, Canada's militia numbered roughly 3,000 and thus an advertising campaign was launched to secure the Canadian Expeditionary Force, and volunteers were encouraged to join a local battalion. This encouragement was quite passive and, to be successful, which initially it was, it relied on the pride of men, to help the cause, to win. As the war progressed and casualties increased, the art of recruitment became more aggressive and also targeted women to persuade men to serve.
Those who did not enlist were deemed cowards. Mass produced posters appealed to men and women of all backgrounds: French and English, Irish and Scottish, young and old, skilled and unskilled, poor and rich alike, each were expected to contribute and leave behind their well-earned conveniences and comforts. Posters were placed in shop windows, on streetcars, alongside vans and upon walls. Combined with speeches, newspaper editorials and lectures at church, the effects of this campaign were staggering: 25,000 men were anticipated, yet 33,000 volunteered to fight.  
By the end of 1914, the government of Canada had increased its commitment to Britain to 50,000 and by the following summer again to 150,000 men, but facing pressure of a daunting war with no end in sight, Prime Minister Borden in 1916 pledged a force of 500,000 men. At the time, the population of Canada was merely 8 million. 
At the Second Battle of Ypres, which lasted from April 22 to May 25, 1915, the Germans attacked using chlorine gas for the first time. The French Algerian Division fled the yellow-green cloud but the Canadians repulsed numerous assaults. Upon inhaling chlorine gas the effect on lungs is severe: within seconds, its vapour destroys the organs, bringing on immediate and fatal choking attacks. For their valiant efforts, four Canadians won the Victoria Cross.
The war to end war, as US President Wilson said, was a becoming war of attrition. Given the numbers being lost on the front, however, the campaign at home in Canada continued and intensified, and throughout 1916 appealed to Asians and Africans, but even these volunteers were not enough to fill rapidly emptying trenches in Europe. Conscription became reality for Canadians in 1917. 
When war began, Europe ruled most of the world. The British Empire covered a fourth of the earth's surface, the Russian Empire a sixth. The French Empire spread from North Africa to Indochina, Germany's from Africa to Samoa. Austria-Hungary was geographically the second-largest country in Europe. None of these empires survived the war, nor did Austria-Hungary.
The United States entered the war in 1917. Although Wilson had been re-elected in 1916 with a promise to the people for the country to remain neutral, five months later he had convinced Congress to declare war against the Central Powers. Convincing the American people required some additional expertise and in this respect within days he authorized the creation of the Committee on Public Information, or CPI, to help spread the virtues of democracy the world over.
Incredibly, by 1918 nearly 100,000 very bright people - a small army unto itself - had been retained and created Uncle Sam, and other famous images to assist volunteerism, and published millions of press releases, bulletins and iconic posters. Not only did Americans eagerly volunteer to fight but they also volunteered their money, giving millions to the Liberty Loan program. CPI was a propaganda machine hell-bent on appealing to the hearts and minds of Americans.
They delivered posters that decried the atrocities of German soldiers that never happened and played to the fears of people, fearing the loss of conveniences and comforts, that by all accounts were wildly exaggerated. Interestingly, as an output of this activity, one young member deeply influenced by CPI was Edward Bernays, nephew of Sigmund Freud, who in fact worked on their campaigns. 
He noted how many people could be converted or diverted due to their passions, acting upon images and symbols, not necessarily their intellect, and how these decisions could after the war be used by the corporations of America to sell just about anything through well planned and executed public relations, augmenting advertising campaigns. Indeed, he was successful.
Bernays was hired by the American Tobacco Company who wanted American women to feel comfortable about smoking in public. He concluded that women needed to see cigarettes as "torches of freedom" that would help emancipate them from the social taboos imposed on them by men. And, after arranging for several young women to walk down New York's 5th Avenue during the Easter parade, smoking, the rest is history, as the story made front page news across the country.