It involved the world far beyond Europe.
As an example going beyond the Western Front:
If the uniforms aren’t a tell, these soldiers are German.
Are they in Germany? No.
Are they in Europe? No.
In fact, they’re a long way from home — they’re in China.
At the end of the 19th century, when the light of the Qing dynasty was fading, two German missionaries were killed in an attack now known as the Juye Incident. The Germans used this as a pretext to seize a fortified bay on the coast of Eastern China.
As a result of their vulnerability, China was forced to concede a 99 year lease of the area to Germany, similar to that of Hong Kong and Guangzhouwan.
In control of the area, the Germans expanded what was a fishing village into an electrificed city, then known as Tsingtao:
When the First World War broke though, Britain was wary of Tsingtao because Germany had based a naval squadron there, one designed to protect Germany’s colonies in the Pacific.
As a result of an alliance signed between Britain and Japan in 1902, Britain requested Japan’s help in dealing with the situation. The Japanese delivered an ultimatum, demanding that Germany withdraw its military forces from Tsingtao and relinquish control of the port city to Japan.
Germany refused, leading to what you see in the first photo — the Siege of Tsingtao.
Soldiers serving under the British and Japanese flags (with aid from a French cruiser) landed in the area, making up a nearly 25,000 strong force. The resulting siege lasted two months and saw nearly a thousand deaths and many more wounded.
Note that “soldiers serving under…” is purposefully phrased as it highlights another way in which this was a world war. Men from colonies all over the world volunteered/were enlisted to fight, and this battle was no exception. A number of Indian soldiers were part of the fighting force, as this photo depicts: