[Zigûr]

Originally Posted by Marwhini

Do you happen to know the location in Morgoth's Ring where Tolkien discusses Morgoth wanting to destroy everything?

It's in 'Notes on Motives in the Silmarillion' in "Myths Transformed".

Morgoth would no doubt, if he had been victorious, have ultimately destroyed even his own 'creatures', such as the Orcs, when they had served his sole purpose in using them: the destruction of Elves and Men. Melkor's final impotence and despair lay in this: that whereas the Valar (and in their degree Elves and Men) could still love 'Arda Marred', that is Arda with a Melkor-ingredient, and could still heal this or that hurt, or produce from its very marring, from its state as it was, things beautiful and lovely, Melkor could do nothing with Arda, which was not from his own mind and was interwoven with the work and thoughts of others: even left alone he could only have gone raging on till all was levelled again into a formless chaos. And yet even so he would have been defeated, because it would still have 'existed', independent of his own mind, and a world in potential.

Morgoth had no 'plan': unless destruction and reduction to nil of a world in which he had only a share can be called a 'plan'.