On our home world, long ago, there were us, the Yeerks, and our hosts, the Gedds. Yeerks are smart and disciplined, but small and helpless. Gedds are big and strong, with hands and feet and eyes, but confused and dimwitted. Gedds came to the pools and put their heads down and told us their names, so their Yeerks would recognize them, and their Yeerks came and helped the Gedds, and helped themselves. With Gedds we built fences around our pools, so predators wouldn't eat us. With Gedds we dug new pools, and invented writing we could see with their eyes. We built them shelters from the rain and fires against the cold. With Gedds we could travel; with us they could create.
Then we met Andalites.
The Andalite Seerow said he wanted to help us: instead of fire, we could have electricity. Instead of fences, we could have metal walls. We could travel across the whole planet, we could write to computers instead of clay. Seerow and his group showed us how to do those things long before we would have gotten there step by step.
We believed them. We thanked them, and learned what they taught us, and built cities and trains and devices. And we filled our cities with Gedds, and met our cousins across the ocean and learned each other's languages, and didn't wonder: if the Andalites are our friends, why don't they want us to know them better? Why don't they bring us home with them to let us see their world, the way they're seeing ours? Why don't any Andalites want to see if we could help them, the way they're helping us - just like us and the Gedds?
We didn't wonder, so we didn't know. But we did think: even if the Andalites don't want Yeerk help, maybe someone does. Maybe some people on another planet is like the Gedds, but without Yeerks. Maybe even better. Not long ago we warmed our hosts by fires, and now we have so much more. Is there even more than that?
And then we made a terrible mistake.
We told the Andalites we wanted to go look. And Seerow said: no. You must stay here. You can have the Gedds, who need you because without you they can barely talk, barely find their way home. But no one else will ever want you. No one else could possibly need you. In the whole galaxy, everyone you meet on every planet will think: disgusting. Pathetic. Get it away from me. It's wrong to even imagine it, and now that I've heard that you have this evil wish, I know I was wrong to even tell you there was life in the stars. Before you can recruit anyone else into your plans I must destroy you. And then Seerow started to kill us.
We fought back, to save ourselves and each other and our Gedds and our cities, and we didn't win, but Seerow didn't either, and some of us escaped. Some of us made it to the stars, to explore, to see for ourselves: was Seerow right?
We found the Taxxons, and Seerow was wrong. Taxxons wanted Yeerks. Taxxons were ruled by their hunger, and could never be free: they would rather belong to Yeerks than to their own emptiness, they would rather work with us than watch their bodies overrule their minds to tear apart their own friends and families for want of prey. We multiplied until every Taxxon could have their own Yeerk, and set ourselves to work on their hunger, which we had adopted as our own the way Seerow never really adopted our problems as his, and today the Taxxons are happier and fuller and hopeful: you can see for yourself if you ever have one as a host.
The Andalites said: you cannot be trusted. Andalite lives are valuable, and Yeerk lives aren't: that means you are at fault for every one of us killed in your escape, and we are blameless, and will punish you. The Taxxons are just as disgusting as you are, and it doesn't matter what they say they want; we'll never believe a word, not when you're in there. You have to be stopped. We will be at war until you stop wanting anything we didn't give you. We will be at war until you die.
We found the Hork-Bajir. And the Hork-Bajir were happy already, but they were strong and sharp and the Andalites would never stop trying to kill us, and we needed them to survive. The Andalites saw that we were growing more powerful, and told themselves they were saving Hork-Bajir, while they ruined their planet and killed them millions in one fell swoop. But we escaped, and some of our Hork-Bajir did too. If the Andalites had their way, there would be no Hork-Bajir left anywhere. One day, when we are not at war, we will not need the Hork-Bajir. We'll be able to explore far enough to find people who want us. Today we keep ourselves and them both safe by sticking together.
We found Earth. And Earth is the most amazing planet yet, full of humans, who are clever and versatile and see so many colors, and we could have said: hello, Earth! We are Yeerks! We can help you! There are so many of you, and you're all so different; do some of you want our help? But if we had done that the Andalites would have said: the humans are just as bad the Yeerks. If they like Yeerks, and prove us wrong, we'll kill them just like we killed the Hork-Bajir, and all the Yeerks with them. So we move on Earth very quietly, very carefully. The humans are strong enough that with them and us together we may be able to finally win the war, and then the whole galaxy will be ours for Yeerks and our hosts to explore together.
Yeerk history by Alicorn