In August 1914 some people believed the war would be over by Christmas.
Military strategists at first expected to use cavalry in mobile warfare, but the chemical and metallurgical industries had created new weapons such as high explosive shells and machine guns, which strengthened defensive positions and made attack almost impossible. Cavalry was of little use in the stalemate on the Western Front, where opposing armies faced each other across fortified trenches.
Elsewhere in Europe there was fighting from Russia to the Alps. An attempt to open a sea route to Russia by landing at Gallipoli was a costly failure. The conflict spread to Africa, the Middle East and even to China.
Both sides looked for innovative weapons and novel tactics to gain an advantage. In April 1915 chlorine gas was used for the first time. New poison gases were continuously developed: mustard gas, phosgene and arsenic shells.
On land, sea and air, military forces employed new technology. At sea submarines made their first significant military impact and U-boats sank over 5,000 ships. In 1917 the first tanks went into action. In the air both sides developed better aircraft and by the end of the war long-range bombers were even able to target enemy cities.
The First World War saw accelerated military developments based on scientific knowledge and industrial capacity. It was the most widespread and destructive war yet seen, and it changed the methods and strategies of warfare completely.