system
Given the following post, respond as if you're commenting on Reddit:
human
[Animorphs] How global was the Yeerk invasion?

The Yeerk HQ was based out of Southern California, but the Yeerks had operated for years. Did they branch out from America and build smaller pools in other continents and countries besides America? Or was the invasion largely localized?
gpt
Their first priority was the United States, because, IIRC, they first learned about Earth in detail by infesting a human abducted by the Skrit Na during the first Gulf War, and said abductee believed that the United States were the most powerful group on the planet. It wasn’t their first encounter with humans (which involved a pair of Americans somewhere around the late 1960s-early 1970s), but it was the one that prompted them to invade after they realised the potential value of humans as hosts.