Dark Earth: The First World War

There are ~36,000 total Entente troops at Tsingtao, backed up by Japanese and British heavy artillery, 6 IJN and 4 RN battleships/battlecruisers and three dragons.

Aircraft are a bit more advanced, being roughly equivalent to mid-late 1916 at the start of the war. Airships and skyships are definitely much more advanced, as those are areas where the impact of Martian technology + space travel have paid off a bit more. Even though powered flight is nominally developed in 1895, the first 15 years are very much experimental, as there aren't the same drivers for urgent aircraft development when airships and cavorite flying machines are present.

There aren't any significant Dominion forces based in Britain pre-war, save for staff and ships fitting out. You are quite right that they concentrate their not insubstantial forces in their own areas prewar. Once war is declared, there is a rather rapid reinforcement of the BEF when it moves to France.

Spain sells their minor islands to Germany in the immediate aftermath of 1898; their courting by the Entente happens after the Anglo-French Entente Cordiale takes place.

German losses are quite a bit higher, as the bombardment is extremely intense. Anglo-Japanese casualties were slightly higher.

The outcome of this particular siege is more of a function of the concentration of firepower from the land, sea and air on a small area, rather than of the size of the world.

Verne writes as a career, which leads to his position of Science Minister. The stories he writes are a bit different, naturally, given the presence of many of the characters.

Verne's From the Earth to the Moon played a role in the 19th Century space race, Around the World in Eighty Days is here a fictionalised version of a real event, Twenty Thousand Leagues Under the Sea is based on real characters, whilst Journey to the Centre of the Earth is an early science fiction.

All of these different circumstances combine to make Verne a writer with an extremely broad array of works, a masterful reputation across many genres and a prescience that brings about his political role.

And by the end of the Great War that number will most likely be in the millions of soldiers and officers.