Other than NCMares fic Night Mares, Are there any decent fics where Equestria is invaded by some *Competent* enemy, and they actually struggle to push them out? Preferably completed?

7407190
SFAccountant's Iron Warriors series comes to mind. It's not so much the ponies fight them off as much as they are forced to team up out of necessity, but it's an excellent series. Several novels, all but one of them complete.

7407190
emkaji's "Equestria: Total War". Although it has been abandoned, I would still recommend you check it out, as I feel it's pretty much what you're searching for.

7407190
EdBoii knows better than I do, but nothing really comes to mind for me. This is partly why I decided to write my own series about such as war.

As far as competent goes, some fics centered around Equestria at War might do since the factions in that lore are almost all more militarily advanced than Equestria. The Changeling invasion of Equestria (mirroring the German Blitzkrieg of 1939/40) is a significant event in game play and one that Equestria (like the Allies in WW2) really has to work hard to defend against.

As far as I can tell, the fantasy setting of MLP doesn't lend itself well to the type military story you're after without some modification to make it more, for lack of a better word, historical.

7407211
Spoilers, Mr. Otterton! I had no idea Equestria would be invaded in Dawn's adventures! If so, then your story is very much so a fine example of a tale where competent military forces clash to repel an invasion!

...and things are about to get a heck of a lot harder for poor Dawn

7407211
EaW fics tend to be brief and pretty focused on individual actions, though. Not to mention most aren't good, imo (the talented writers interested in the settings are probably occupied working on the actual mod).
Having said that, if fics of short length and scope are also an option, then there's Antiquarian's "Memoirs of my war" and "Hold the Line" which kind of fit the request (if one interprets it very liberally at least).

https://www.fimfiction.net/story/471474/of-cloaks-and-daggers

I thought this was decent, it's anthro though.

7407190

Do border skirmishes count?

TRedheart's War

• MLP: FiM
• Adventure
• Drama

A nurse has seen it all. A combat medic has seen even more.

• Gore
• Violence
• Celestia
• Cadance
• Shining Armor
• Nurse Redheart
• Hippogriffs

SockPuppet · 46k words  ·  462  15 · 5.1k views

This and it's sequel is without a doubt the best I've read on that front. The first story is essentially basic training to get you to know the characters and the second is where the war starts.

Rise of Firefly

7407190
Can'terlot comes to mind but was not finished. There are abaut 3 or 4 proper arcs done and its not pulling any punches. If you dont puke from abberant monsters, go for it.

I know a lot of Command & Conquer crossovers involve invasions, either humans or Scrin (aliens) but quality is a tossup from fic to fic and only a handful of them are actually completed.