So, on the planet of Episol live the species Episolians. They have conquered and enslaved most of the galaxy, and recently they have laid eyes upon a planet called Earth, with a primitive species they plan on conquering. On stardate 22.34.68 a force of 50,000 Episolians, leaving with 100 gunner ships, 25 battleships and 5 carriers leave to conquer Earth. The send a small scout unit to recon Earth, and when news comes back about Earth, every soldier is terrified.
The scouts, when entering the Sol System, passed 4 gaseous planets before reaching Earth. On the way, when they passed Neptune, they saw a humongous starship twice the size of anything their species ever made. They landed on Earth, with their magnetic proton launchers in paw, and saw the humans for the first time. They were massive behemoths, many times the size of any Episolian. The Episolians were the size of human basketballs, and looked like balls of fur, just like a tribble. When they tried to fight the humans, their weapons caused mere blisters, even the cannons they had only caused sprained ankles and the occasional compound fracture.
An Episolian in Earth gravity weighs up to 2 pounds, and a human infant can crush them easily. The Episolians yelled and screamed at the humans for mercy, as they were being picked up and stroked to death, but the yells of agony just sound like purring and vibrating to the humans. The humans also live for over 1,000 cycles (80y) while Episolians only live 100 (8y).
So my question is, given their shortcomings, how could the aliens conquer humanity?
Details about invasion
From radio reports made by humans, the Episolians decide to invade the most powerful human nations. Those are the USA, USSR and China, along with a small detachment in Europe, mostly the UK and France. They cannot voyage into Siberia, as it is far to cold for them. Water deeper than 8 feet is also a problem if they’re on foot, as well.