The story is at least partially written in a flash-back. The protagonist is a senior military commander in the Terran space fleet (forget the actual name).
An alien race, described as very man-like, arrives on Earth. They are man-like, but larger and more muscular, than a typical human. There is also something unusual about their faces. I think the features are somewhat rougher than those of human beings, don't change expression as easily, or perhaps all of them look similar to each other. Some combination of that, as best I can remember.
The aliens are a warrior race, who have mastered FTL travel, and have conquered many star systems. When they arrive at a new world, as they have with Earth, they offer two options. First, the world can submit to them, and enjoy the status of a favored thrall (I believe that is the term used). Second, the world's people can try to resist, in which case they will be brutally conquered and enslaved. Rebellion or betrayal of the first option also leads to the second outcome. IIRC, these first aliens are only emissaries with one or two ships, but a huge armada is waiting to take possession of the system.
There is much debate by humanity over what to do, but in the end, the perceived technological superiority and resources of the alien invaders is such that submission is the only sane option. The protagonist, writing in his journal, accepts this with resignation. One of his peers, a hot headed type, is outraged that humanity has given up without a fight.
The "doom" comes when the protagonist learns that the hot-headed admiral conceived of a plan to stop the alien fleet as it entered the system. The Terran space fleet has been taken behind one of the outlying planets or gas giant moons. Under the command of the hot-headed admiral, the alien armada is ambushed. All comes to naught, however, when it is discovered the alien ships possess a force field that renders them effectively invulnerable to anything in the Terran arsenal. The entire Terran fleet is destroyed, and the enraged aliens head towards Earth.
The story closes with the protagonist writing of the events in his journal. He sees a number of alien warriors closing in on his location. He comments on their facial features, saying "they don't look - " the story breaks off mid-sentence, implying the protagonist has just been killed.
Timeframe of Publication
I read this in some old anthology. I can't remember when I read it (90's, maybe?), but it was clearly an older book. I would guess 1960's or earlier.