The aliens are seeking to build a colony on Earth. Reasons could be overpopulation, destruction of their own homeworld, etc. Earth does not necessarily have to be an ideal environment for the colonizers.
The alien psyche is basically insecure and they like to make themselves feel big by ruling over other species.
The aliens are only concerned with Earth's resources. Presumably this would include resources limited to inhabitated planets (eg. food sources, etc.)
The aliens are using Earth as a practice planet in preparation for the real invasion elsewhere.
The aliens were actually peaceful explorers until one or all of the Earth's nations launched orbital nukes at them. Now they're pissed...
"Hey, Balkizorg, I'm bored. Why don't we invade that planet over there?"
The aliens are gradually weaning off invasions and are now doing short invasions of backwater worlds with plans of enventually moving on to unihabited asteroids...
(Hey.. do you have your M class planet yet?) or some other contest. (If you can conquer the Earth..... A brand, New, Imperial Star Destroyer!)
Jason Che-han Yip contribitued number 7 firstname.lastname@example.org
Arvind Knudsen contribuited number 8
The Preserver contribuited numbers 9 - 15
Aliens_Invading.php -- Revised: January 27, 2021.