First of all, that's obviously not footage of an actual game considering he started in Discovery Age, has about 350 population when he should only be able to support 10, and has about a million of each resource.
Second, if I were you I would refrain from basing my complaints about a gameplay mechanic that was removed in order to rework it on a video made before it was reworked, when I haven't actually seen the result of the rework yet.
Third, it is altogether incorrect to think of the Great War as a sixth age after Imperial. Rather it acts as a stalemate-ender, similar to Revolution but much harder to obtain, that gives you the technological edge needed to destroy everything and thereby end a game that's going on too long.
Of course, it is not an actual game. That's why I suspected that it might be scenario editor.
Anyway, thanks for the information. So, only European(including Balkan) and Anglo civlisations get access to great war units?