Populating lists of military units

Populating lists of military units from all the countries involved in the First World War is a huge task.

1 Albanian units in World War I
2 American units in World War I
3 Australian battalions in World War I
4 British battalions and regiments in World War I
5 Canadian battalions in World War I
6 Chinese units in World War I
7 French units in World War I
8 Greek units in World War I
9 Indian battalions in World War I
10 Italian battalions in World War I
11 Montenegrin units in World War I
12 New Zealand battalions in World War I
13 Portuguese units in World War I
14 Russian units in World War I
15 Serbian units in World War I

Australian battalions in World War I

Should be complete for infantry; many non-infantry units have been added but additional ones could be added from the list at https://www.awm.gov.au/units/ww1/

British battalions and regiments in World War I

Includes Irish units; most infantry regiments should be in but the huge task of adding the battalions for each remains. There's a list of British divisions in World War I based on Wikipedia, and a good reference for the size of the task is this Great War Forum post listing divisions (for reference when looking for unit diaries).

A good source for detailed battalion listings is the Long, Long Trail's page for the British infantry of 1914-1918