Triplanetary

In this prequel to the famous Lensman saga, battle is joined for the control of the universe.
The Arisians, benevolent humanoids, who have declared themselves Guardians of Civilization, are waging a cosmic war against the Eddorians, a race of creatures who seek to control and enslave the sentient races in our galaxy.

Now their battleground is a planet in a remote corner of the Milky Way: Earth.