Horses were first introduced to North America during the Spanish conquests of the early-1500's, and by the 1600's, the First Nations of the Great Plains were using horses in warfare and in hunting to such success that horses became intertwined in their respective cultures.

When the Dominion of Canada government first began to colonize western Canada, it sent the North West Mounted Police west on horseback in 1874, while nearly 1,800 horses were used by Canadian soldiers during the Northwest Rebellion of 1885.

During the American Civil War (1861–1865), it is estimated that as many as one million horses were used by the Union side alone. In total, as many as 1.5 million horses and mules were killed during the war.

The British War Office shipped 620,000 horses, mules and donkeys to South Africa during the South African War, also known as the Anglo-Boer War, (1899-1902). Canada provided over 16,000 horses for that campaign. Another 5,000 Canadian horses were shipped to South Africa for use by Canadian troops.

Horses, mules and donkeys suffered terribly in South Africa, a result of the extreme change in climate and the forage available to them. Of the British horses that died during the South African War, over 325,000 horses and 51,000 mules died of starvation or illness and disease because of their poor diets.

In no other time in history have animals in service suffered so much as they did during the First World War. Much like the hardship the soldiers themselves suffered, the animals that supported them had to work in the terrible conditions created by harsh weather conditions and relentless artillery strikes.

Nations fighting in the First World War, including Canada, relied on horses and mules to transport ammunition, artillery, food, soldiers, and the wounded; essentially, all the material required to wage war was hauled by horses and mules at some point in its journey to the front lines. Trains and vehicles, such as lorries or trucks, were essential to the transportation networks, but in the muddy First World War battlefields, motorized vehicles were often useless.

The First World War began on July 28, 1914 and within the first twelve days, the British Army bought 140,000 new horses, in addition to the 25,000 horses it already owned. Canada's permanent force, meanwhile, had only 270 horses when the Canadian government declared war on August 4, 1914. But when the first contingent of the Canadian Expeditionary Force (CEF) sailed for England in October 1914, it carried with it 7,600 horses along with the 31,000 soldiers.

A further 50,000 horses were shipped from Canada to Europe between 1914 and 1918. It was a small number, however, compared to the 1.2 million animals Britain and France purchased from the U.S. In all, it's believed that Britain and France combined required over 2.5 million horses and mules during the war.

It is estimated that as many as eight million horses were killed on both sides during the First World War. Almost 500,000 horses and mules in the British Army died or were killed in all four years of fighting. Gunfire (small arms and artillery) was a hazard horses and mules faced, and yet, disease, illness and exhaustion led to the deaths of more horses and mules than bullets or shells.

Life was not easy for horses and mules in the war, especially the draught and pack animals. They faced terrible, dangerous conditions. Like the soldiers stuck in the trenches, horses and mules lived in mud and water often with little to no shelter, especially in the winter of 1916-17, which was particularly harsh.

Heavy rain and snow, coupled with heavy shelling and constant movement by men, machines and animals churned the soft, waterlogged land of Flanders into a quagmire. It wasn't uncommon for horses and mules to disappear into the mud.

Equines also saw their "heaviest work" of the war during the winter of 1916-17, at times hauling supplies and ammunition for up to ten hours at a time without food or water as the Allied forces prepared for the Battle of the Somme and the Canadian attack on Vimy Ridge and then Passchendaele. Many draught animals unable to cope with the strain died of exhaustion.

A lack of shelter, food and clean water meant horses and mules were always cold, exhausted and hungry. They also suffered from organ failure, shell shock, and intestinal and skin diseases. Parasitic mange increased dramatically. Veterinarians were forced to clip the coats of horses and mules under their care despite having to leave the animals with no natural protection against the elements.

When veterinarians were able to provide shelter, food and water, the horses and mules of the Canadian Corps (and the rest of the armies) tended to do quite well and after that terrible winter of 1916-17, animals in Canadian Corps were much healthier. In the following winter, they even gained some weight.

Similarly, when veterinarians could treat wounded or sick horses and mules most of the animals could be healed. On average, of the 2.5 million horses and mules treated by veterinarians, a majority went back to the Front when they were healthy.

The British Army and its allies, including Canada, had a huge stake in keeping their horses and mules healthy for without their transport power, the war could not have been won. At Passchendaele, alone, Canadian artillery fired 1.4 million shells during October and November, 1916 most of which was hauled by draught horses and mules as vehicles were largely useless in the boggy mud.

By war's end in 1918, despite the First World War seeing the introduction of motorized vehicles on the battle field, the British army had 900,000 animals versus 35,000 motor vehicles. Canada, had 24,000 horses and mules at the time of the armistice.

Warrior lived a charmed life. He was one of the few horses that survived all four years of the First World War despite being at the front lines throughout most of the war.

Because of his luck, his numerous close calls, and his calmness in the face of battle, the Canadians of the Canadian Cavalry Brigade came to call Warrior "the horse the Germans couldn't kill".

But not for lack of trying: Warrior and his rider could have—should have—been killed or wounded many times during the First World War, yet both escaped the war safely even though neither Seely nor Warrior were ones to remain safely behind the lines.

Warrior and his owner and rider, General Jack Seely, commander of the Canadian Cavalry Brigade, took part in all the worst battles of the war, including Ypres, the Somme, Paschendaele and Cambrai. Warrior and Seely also led the cavalry attack at Moreuil Wood in March 1918.

Recognized as the last great cavalry charge of the war, it forced the German army to withdraw, stopping the German spring Offensive. A quarter of the Canadian cavalrymen and half the horses involved in that charge were killed or wounded, and yet both Seely and Warrior made it through uninjured.

Twice, Seely had different horses he was riding shot out from under him while Warrior was recovering from illness. Warrior, meanwhile, survived getting trapped in deep mud, shot at by aircraft and snipers and twice having his stable collapse upon him after being hit by shellfire.

Remarkably, shellfire seemed to create little fear in him. Seely wrote "On many, many days... during the four years that were to follow I rode Warrior in shell fire, sometimes so heavy that he was almost the only survivor, but never once did he attempt to bolt or to do any of the things which might be expected of an animal reputed to be so naturally timid as the horse. No, my stout-hearted horse not only kept his own fear under control but by his example helped beyond measure his rider and his friend to do the same."

Even though Warrior and Seely led the Canadian Cavalry, neither were Canadian: Warrior was born on the Isle of Wight, and Seely was a British Member of Parliament before the war.

Given their willingness to put themselves in danger and their coolness under fire, the Canadian cavalrymen grew to love both Warrior and Seely. However, as Seely jokingly pointed out, the Canadians were much more impressed with warrior for whenever he and Warrior arrived, the cavalrymen would never say "Here comes the general" but rather "Here's old Warrior".

Warrior lived a full life after the war. He and Seely retired to the Isle of Wight where both, but especially Warrior, were treated as celebrities. Seely wrote a book about Warrior that was published in 1934. His grandson, Brough Scott, re-released that book as My Horse Warrior: The Amazing Story of a Real War Horse, in 2011.

Warrior died in 1941 at the age of 33. The Times published an obituary to one of the greatest warhorses to have served in the First World War. In 2014, Warrior, chosen to represent all animals that served in the First World War, received the first and only Honorary PDSA Dickin Medal.

Once the First World War ended on November 11, 1918, the Canadian government sold its 24,000 horses and mules (12,000 draft horses; 7,000 cavalry horses; and 5,000 mules) to the Belgian government, which in turn sold the animals at auction. Of those, 1,245 horses were slaughtered for the meat. The rest appear to have been bought for farm work, for riding, for draught work within cities and towns and for the reconstruction of Belgium cities and towns.

The British War Office, meanwhile, which owned 900,000 horses, mules, camels and oxen in all theatres of the war sold 40,000 horses and mules to butchers from 1918 to 1920. Another 200,000 British animals were sold in that period, as well.

Of all the horses and mules that were taken to Europe from Canada, only 110 horses, chargers belonging to high-ranking officers were brought back to Canada. That number, however, does not include the animals, such as the goat "Sergeant Bill", who was mascot for the 5th Canadian Infantry Brigade, and smuggled aboard ships as soldiers returned home.

As British horses and mules fared no better, animal rights organizations, such as Our Dumb Friends' League, sought out and bought former British Army horses, easily identified by their arrow brand, often "overworked and emaciated", and found them homes where they could "live out their lives in comfort."

A similar initiative took place in Cairo, Egypt in the 1930s, as well, but given the age of the horses and their poor shape, most were killed to put an end to their suffering and give them peace after what amounted to long, hard lives toiling in the war and heat of Cairo.

The end of the First World War did not bring about the end of animals in warfare. Horses, mules and donkeys still played a surprisingly large role in the Second World War, despite it being a mechanized war reliant on tanks, trucks and airplanes. In fact, the number of horses, mules and donkeys used in the Second World War may have outnumbered those used in the First World War.

In 1939, the German Army already had over 500,000 horses in use. By the time the war ended in 1945, Germany had 2.75 million horses, of those, 1.5 million were killed or wounded. The Soviet Red Army, meanwhile, used 3.5 million animals during the war, including dogs trained to run under German tanks while carrying explosives on their backs. An antenna set off the explosives when it brushed against the underbelly of a tank.

Perhaps the oddest use of animals in warfare came when the U.S. developed its "bat bomb" program. The idea saw tiny incendiary bombs attached to bats that would be released over Japan. When the bats roosted in buildings the bombs would explode creating a multitude of fires. The project proved to be effective but was cancelled in 1944 in favour of research on the atomic bomb.

In Italy, Canadian soldiers relied upon mules and donkeys to transport supplies, including ammunition, through the rugged mountain terrain. Capt. L.G. Alexander, medical officer for Calgary Tanks wrote in his journals that on Dec 15, 1943, near San Leonardo, Italy, mules were used to bring shells up to the Calgary's' Sherman tanks.

"Again, no change in the combined 'A' and 'C' Squadron position was reported. Tanks remained on their positions all day to give support to the infantry should it be required. Supplies on the 'B' Squadron sector were running short due to the fact that the roads to this position were under constant shellfire, and cross-country routes were impossible for the wheeled or tracked vehicles owing to the deep ravine to the rear of the position. Accordingly, it was decided to bring up a mule train consisting of 40 mules." he wrote.

"Under cover of darkness, the train left the 'A' echelon area and proceeded across country to the 'B' Squadron area. Out of the 40 mules that started, only 18 arrived at the Squadron area which was reached at approximately 2100 hours. However, these relieved the immediate shortage."

But even in modern warfare and its technology, there are still times when equines are still used. Canadian soldiers, for example, used donkeys during the recent conflict in Afghanistan, to haul supplies and equipment in the rugged and often mountainous terrain of the country.