The Spice

So, insterstellar combat will add some spice into the JTAS-K on the trip between the Kobra Worlds Sector, the Jerlea Ringworld Sector, and the Urbanos Sector. In Urbanos, the ultra-high-tech alliance includes the humans of Minerva and Urbanos, the humans and Dolphins of Fronomios, the ancient Bushi avian race, and the creature know as Mmmm. They are in conflict with a super-deadly race of microscopic viruses known as "the Riders", who take over humanoid bodies and wage war on the "free humans". This map below shows how the conflict is progressing, with the Oceanic Alliance losing the war on both fronts. The second front is a force or alien race, that I haven't decided yet. I am looking for some advice in that area since waging war against a bunch of ultra-tech worlds (TL18-20) is extremely difficult at best. And yes I know Mmmm and the Riders are from GURPS, I just love them too much to not include them in my new universe. I will most likely take them out later, or just rename them, but for now they stay.

So who is the second race/power invading from the south east? Give me some ideas, people :)