The death toll is still difficult to comprehend: an estimated eight million soldiers were killed and millions more were maimed, in a war that transformed the way nations fought each other.
The mother of invention
It seems absurd in hindsight but, in mid-1914, military experts expected the major offensives of World War I to be led by cavalry charges. They could not have been more wrong. By the winter of 1914, a continuous line of trenches ran 450 miles from the Belgian coast to Switzerland. Moreover, this line didn't substantially shift until the summer of 1918.
Nearly a million British and Commonwealth soldiers were killed in World War I. Almost 300,000 have no known grave. Professor Margaret Cox is determined to make a difference. Using modern forensic techniques, she helps the Ministry of Defence identify some of the dead.
Tragically, the killing didn't stop in 1918. The 20th century was the bloodiest mankind has known. Millions died in scores of conflicts, leaving behind millions of grieving loved ones.
When the Allies landed on the Gallipoli peninsula in 1915, the Turks were waiting. The disastrous campaign led to 250,000 Allied casualties and the man in charge almost lost his job. That man was Winston Churchill.
The King's business
Britain entered the First World War on August 4, amid a huge wave of patriotic fervour. Young men enlisted in droves, eager to take the King's shilling. The concept of a muddy, bloody death in the trenches had not yet been born.