Every ten years, now even less.
1990 - Oil Price Shock / End of Cold War, reduction in defense spending
2000 - Dotcom bust
2008 - Housing Market crash
2020 - COVID
2025 - Trump just being a fucking dumbshit who wants to tear down everything other people built
You know, you're right. I had this weird false memory of there originally only being three of them and that the yellow, green, and black rangers came later. I just checked Wikipedia, and she was for sure in the first episode.