Let's Talk Morgoth

[Maédhros]

Eru's intervention at the Sammath Naur is subtle, & the event may be seen as a fluke - Gollum simply overbalances - by those who wish to see it that way.

I would like to know how can you be so sure that it was Eru's intervention and not just mere luck.

Of course, this opens up another can of worms - if Melkor hadn't rebelled, & thus created an alternative to Eru's divine plan, would one of the other Ainur have rebelled instead? What I mean is, Melkor's rebellion sets out an alternative & therefore introduces choice into the 'game'. At that point the Ainur have to decie whose wide they are on. If Melkor hadn't done that, would one of the other Ainur have started wondering about 'alternatives' & hence become 'Dark Lord' instead.

I don't agree with this. How can anyone know that because Melkor rebelled that it was an alternative Eru's plan?
I see it in a different view than most. People tend to look at what Arda became as the way the Plan unfolded. I just think that that was only a process that eventually led to Arda Remade which was the true End or Arda so to speak.
If Melkor or another Ainur had rebelled or without any rebellion, I believe that in the End the Arda Remade in the Melkor intervention would have been the same as if other or no intervention, but the specific path into which it evolved would have changed entirely.
And did Melkor really rebelled?
Ilúvatar gave him the powers and the freedom to use them as he saw fit. It was his right to act as he saw fit, as where the other Ainur.