The Delta Quadrant is the least explored and outermost region of the Galaxy for the Federation. Coincidentally, the USS Voyager was transferred there, which on the way back explored much of the quadrant and made many first encounters.
Powers: The main force until 2378 was the Borg, who controlled almost 2/3 of the quadrant through the transwarp network. However, many events weakened their forces: the invasion of race 8472, the destruction of the transwarpuzel and tunnels, the destruction of Unimatica 01. What will be the impact on the distribution of forces in the future is a question.