The Bajorans are perhaps an example of a species that was greatly affected by failure of Cardassians (and, depending on how you view it, the Federation) to follow anything like the Prime Directive. According to Memory Alpha, the Bajorans had developed "sublight space travel" when they were "annexed" by the Cardassian Empire; as such they were a pre-Warp civilization and fell under the Prime Directive.
The Bajorans were enslaved and their planet's natural resources were plundered for forty years. They had a Resistance, but neither Memory Alpha nor DS9 (which starts right after the occupation ends) detail exactly how a technologically inferior race was able to expel an established occupation, or whether they had help from the Federation or others. The Federation then set up a friendly presence on the former Cardassian space station, originally to provide administrative and scientific assistance in the Bajoran recovery.
While the Bajorans do have some sort of military (the Bajoran Militia), it seems to be relatively weak and perhaps technologically inferior to others. In the first episode of DS9 Season Seven (Memory Alpha doesn't really go into detail on this) Kira, with the militia's backing, confronts a semi-hostile Romulan warbird, and everyone involved - Kira, the Romulan officer, and the Federation officer present - considers the Bajoran vessel greatly outmatched. So it seems likely that they are still technically a pre-Warp civilization, despite their significant role in 24th-century events.