How did the Borg fall?

Could you elaborate on the circumstances surrounding the downfall of the Borg? It seems like a significant event, yet the details remain murky. Was it a sudden collapse, or a gradual decline? Did internal conflicts play a role? Were there external forces at play? What specific events or decisions led to this moment? The Borg, once a formidable power, seem to have vanished into obscurity. What are the key factors that contributed to their fall from grace? I'm eager to understand the full picture behind this enigmatic tale.