"Together, my lord Sauron, we shall rule this Middle-earth. The old world will burn in the fires of industry. Forests will fall. A new order will rise. We will drive the machine of war with the sword and the spear and the iron fist of the orc."
The orcs could be looked at as an allegory of the faceless, dehumanized, industrialized proletariat, people who had sold their soul to the machine. They can be seen crafting huge weapons of war, siege engines and such, in giant factories fueled by those coal deposits.
The reason the industrial revolution never happened in Middle Earth is because the Fellowship of the Ring prevented it.