Yeah I am honestly unsure if all the destruction saruman caused to his area was solely to setup his war machine. Meaning he needed to make enough armor and weaponry for his vast army, and making 10k swords, 10k breastplates, 10k etc etc etc, takes either a lot of time, or a lot of people working together. He had a lot of people working for him, but had to bring in an insane amount of raw materials and create a lot of space for them to work in. So he strip mined the surrounding area for every resource and then spread out into fangorn when that wasnt enough. Which is what led to his downfall since it was cutting down fangorn forest trees that pissed off the ents so much.

I dont know if his uruk hai were suggested to be created by some pod person process or just some insane cross breeding experiment that involved using thousands of slaves and such.