why is that people assume that a fictional military force in the future--especially an alien one in this case--must follow modern day American military practices.
It's not "people" who appear to follow those in Star Trek. It's the Universal Translator, which puts the word "Major" in Kira's mouth when she describes her position within the Bajoran militia system. For that matter, it puts the word "militia" in there, too - and probably even "Bajoran" and "Kira".
If one studies the history of those ranks, they all evolved
...And kept on evolving. So there currently is nothing left to identify "Major" or tell it apart from "Colonel" save for the fact that the current system treats them as two rungs on the rank ladder, separated by one further rung called "Lieutenant Colonel".
Nothing about Kira's job yells "Major" as such. What she usually does could be done by a Lieutenant or a Lieutenant General alike, were she to be employed by the US Army. It's just that she isn't. She's doing fictional space duties that on one hand have more strategic value than the US President holds in his fingertips when fiddling with a certain briefcase, and on the other are more mundane than the daily maintenance of a 5-ton truck.
So the only reason Kira is a "Major" for Sisko may be that she stands on the fourth rung of the Bajoran rank ladder. That rank may be known to the Bajorans as "Fourth Naysayer", literally, as historically the duty of Bajoran officers was to tone down the power-mad orders of their absolute superiors; or something like "Servant to General's Advisor", which is what the role became fifty thousand years later. But the UT doesn't bother with such nuances, which would be futile anyway because the definition has kept on evolving and currently the rank reads as "That Who Tried to Grab Postwar Power But Failed to Attain Colonel and Was Too Good for Lieutenant and Too Controversial for Captain".
That said, I'd love to take the "Roman" ranks of Cardassia and Romulus at face value, their curious English translations literally meaning e.g. that a Romulan Centurion does the very same thing a Roman one did (commanding one cohort or another, with a better or more prestigious cohort indicating higher standing) and isn't just a fancy way of saying "Sergeant". Whenever other cultural references slip in, such as the Romulan "Sub-Lieutenant", they would be taken at face value, too, closely approximating that other culture. And whenever we get something alien, like Glinn, it is there to tell us that this particular part of the Cardassian system does not follow the old Roman model that the other ranks might suggest.
As we saw, the Cardassians generally did not leave usable hardware behind.
But I think we saw the reverse. In their confusion, they did leave DS9 behind, either with the intention of reclaiming it ASAP, or because they didn't really plan for defeat and had little idea what to do. They left Garak behind, and he soon became a Bajoran asset, too. Both assets could have been programmed to kill their new masters brutally and efficiently, or worse, but the Cardassians fumbled it and Terok Nor's feeble attempt at evicting the Bajorans in "Civil Defense" was thrwarted.
Against that, it doesn't seem implausible at all that Tahna Los in "Past Prologue" or General Krim in "The Siege" commanded abandoned Cardassian warp transports, or that the other triangular ship type seen in "Ensign Ro", "A Man Alone" et al. was also of Cardassian make. We could of course alternately think that the Cardassian convoy in "Rules of Engagement" utilized these two ship types because Cardassia was depending on Bajor for its warp transports...
Timo Saloniemi
