Hello. I was looking through the GOG catalogue for a strategy game where the action happened during the Great War (i.e. the First World War), either in full or in part.
I can find many, many games related to the Second World War (or "future" wars), but the first World War seems quite under-represented. Maybe it is not "sexy" enough?

Could anyone point out a relevant game I may have missed? Thank you.

There is a WWI scenario for Civilization IV made by Jon Shafer (co-designer of the Beyond the Sword expansion pack and future lead designer of Civilization V): https://forums.civfanatics.com/resources/wwi_jon_shafer_bts319.22527/

The Battle Isle Platinum Collection has History Line included, a great strategy game, although a bit older. Includes a bit of "history" between the missions.

Funny, I was looking for some the other day myself and they really are few and far between in any genre. Most of the ones that do exist are gimmiky shooters, alternative history or multiplayer only affairs.

Darkest Hour: A Hearts of Iron Game is supposed to allow you to play from the Great War through to the Cold War. I've never played it so I can't say much more about it.

One of the greatest WWI games is not on gog yet. The Darkness, brilliant game, with great War Levels. There is even the heavy gustav in it.

There's "The Last express", an adventure set just before the start of the war in 1914:
https://www.gog.com/game/last_express_the
Haven't played it myself and it might not be very good, though iirc the historical setting was lauded at the time.
WW1 probably isn't considered suitable material for games because of its negative image as a futile war that didn't solve anything and consisted of unheroic mass death in idiotic infantry assaults against entrenched positions defended by machine guns. That just doesn't sound like fun.

Partial exception might be the air war which seems more glamorous and chivalric than being blasted by artillery, machinegunned or gassed, e.g. there was the Red Baron flight sim:
https://www.gog.com/game/red_baron_pack

I know it's not a strategy game, but I'd still I'd like to call attention to 1916 DerUnbekannte Krieg. Yes, it's about dinosaurs. But no, it's not a fun, silly game, it's actually really damn effective and creepy.

Victoria covers the timeframe from 1836 to 1936, if that helps.

https://www.gog.com/game/victoria_complete

The setting and idea are pretty good. Unfortunately, it was done by Americans and it's noticeable. Rather than having a contemporary/"realistic" view on the whole thing, it's from a modern perspective, looking back at the events through the eyes of an American protagonist. I actually did have some hope when early on the French train personnel talked about taking Alsace back in the upcoming war but after that, it kinda swung in the total opposite direction.

I seem to remember there was quite a few 90s flight sims in WW1, like Dawn Patrol. Was it though? Without Austria egged on by Germany there wouldn't have been a war. Without British involvement would The Central Powers have dominated Europe for a century or more? Who knows how the world would be different. There are interesting scenarios at play here. And then does Austria/Germany become democratic? Or not? Does colonialism stay in this timeline?

We know the horrors of these wars but different types of horrors could have happened without them.

Red Baron, Knights of the Sky and Wings are WW1 flight simulators.
Empire Earth has a WW1 scenario.
Iron Storm and Necrovision are alternate history WW1 fps's.

And it's a really good one. Unfortunately it's just a few missions.

Not on Gog, but DRM-free too:
http://fireflowergames.com/shop/world-war-i/