Coming in a little late here, but, as far as the Third Age goes, I think the principal 'block' was the presence of the Rings. They were designed with the purpose of 'preserving' the natural world against the depredations of Sauron, but also to 'stop time'. Galadriel desires to live in a place where the flowers & trees do not die.
The 'preserving/embalming' effect of the Rings in Lorien & Rivendell would surely act as a brake on progress, & the effect of such powerful objects as the Elven Rings would surely 'bleed out' into the world around. Also, do we know how many lesser Rings, made with the same power & intent were 'floating around' in ME? Aside from the physical effect, would there not also be a psychological one, affecting the way the people of ME thought, slowing their desire for progress, & leading to a backward looking idealisation of the past. When the One is destroyed, the effects, physical & psychological, of the Rings was disipated, allowing change/'progress' to begin in ME.
|