The Engaging

"The human population was spread thinly in small tribal groups with just a precarious hold on the planet, so the aliens came up with a plan that would enable them to colonise the planet, with or without the knowledge or consent of those humans. They might not be in favour of genocide, but should the few and very primitive humans dwindle and die off, did they care? To attempt to blend in with these humans to establish themselves, the aliens constructed small devices that enabled the wearers to appear human. But it was never to be. The other factor was more effective than clubs and spears. The smallest creatures – germs, managed to sneak past this advanced race's defenses and killed the crew, but not before the commander managed to send a full and factual report back to the fleet that lurked a very long way away." ― excerpted and quoted from this book's product page on Amazon.com as of 2020-03-09.