[The Saucepan Man]

There was really only one strategy: get the Ring to Mount Doom and destroy it. And that strategy was devised by the wise present at the Council of Elrond, most particularly Elrond and Gandalf. And it was a strategy that bore little hope, as Gandalf recognised.

As to how the strategy was put into action, well each of the characters played their part, even (or should I say especially) Gollum. Indeed, even Sauron had a hand in it, since it was he who had the blind spot as far as Hobbits venturing into Mordor were concerned, and he who fell for the ruse of concentrating his attention on the Black Gate when he should have been looking at Mount Doom.

Yes, it was all part of Eru's will, but it was for the free peoples to accomplish the task, with a little assistance of course - indirectly in the case of Gandalf (and perhaps the Eagles), and more directly in the guise of providence.