R. Star wrote:
Though this gets problematic when you analyze just how the Klingons were able to invade or the Romulans were able to open their own second front against Cardassia.
Not necessarily. The maps are only 2D representations of known space. They don't take into account territory or borders beyond the plane of the computer monitor. It's possible both the Klingons and Romulans share a border with Cardassia that's above or below the plane in question.