In "Ensign Ro", Captain Picard tells a Bajoran refugee leader that the Federation expressed sympathies for the Bajorans, but was unable to intervene due to the Prime Directive.
If this was just some skirmish between a couple of non-aligned planets, that would make sense. But the Federation was at war with the Cardassians in the 2350s and 2360s. In the 19th, 20th, and 21st centuries on Earth it was common for belligerent powers to supply terrorist and guerilla groups with weapons, advisors, and other support when those groups were fighting their enemies.
And the same thing happened during the Federation-Klingon conflicts of the late 2200s. The Klingons attempted to take over the strategi