Books series where aliens are associated with classical elements

Question

I remember reading these books a long time ago.

• In each book a new alien race is discovered.

• Each alien race is associated with a classical element: fire, water, etc.

• They fight each other while Humans (or a humanoid race) is stuck trying to deal with the fallout.

• There were about 5 books in the series.

• I think the "fire-type" aliens where called the Furios(?) or something similar if that helps.

Answer 1

This is The Saga of Seven Suns. There are actually seven books.

The elemental aliens are the

1. hydrogues (air)
2. faeros (fire)
3. wentals (water)
4. verdani (earth)

There are other, non-elemental aliens: the Ildirans and the extinct Klikiss.