The Trozonians are an ancient speicies who lives on the other side of the galaxy. Somehow they know of the Federation and believe that it will take over the galaxy one day.
History
A ship was sent that took 248 years to get to Earth, so that it would destroy it. But the attempt was thwarted by the USS Phoenix-X. On their way into Federation space, they disabled ships like the USS Cedar, the USS Blue Nose, the USS Shark, the USS Sun Light, and the USS Grolier. (PNX: "Bio Level 4")
Ancient Holy Scriptures
According to thier scriptures, which are nearly 6000 years old - it was prophesied that the homeworld of Trozonia would be taken over by the Human species.