When did BMX start?

I'm curious to know, when exactly did the world of BMX cycling begin to take shape? Was there a specific year or event that marked the inception of this exciting and adrenaline-fueled sport? And what were some of the early developments or milestones that contributed to its growth and popularity over time? It's fascinating to think about how far BMX has come since its inception, and I'm eager to learn more about its rich history and evolution.