Sauron's Great Miscalculation

[Boromir88]

Originally Posted by Zigûr

After all, despite how duplicitous the Mouth was being in any event, there was no one present to represent two of the major powers of the North, Erebor and Dale, who would have come under Sauron's 'East of the Anduin' dominion.

A week prior to The Black Gate there was the Battle of Dale where King Dain is slain, and King Brand, with the remaining dwarves and men hold up in Erebor and are besieged. So it's probable Sauron already felt assured Erebor and Dale under his dominion (or was about to be).

And prior to The Council of Elrond, Sauron already sent a messenger to make an offer to the dwarves of Erebor, in exchange for info on a Baggins:

'At this we were greatly troubled, and we gave no answer. And then his fell voice was lowered, and he would have sweetened it if he could. "As a small token only of your friendship Sauron asks this," he said: "that you should find this thief," such was his word, "and get from him, willing or no, a little ring, the least of rings, that once he stole. It is but a trifle that Sauron fancies, and an earnest of your good will. Find it, and three rings that the Dwarf-sires possessed of old shall be returned to you, and the realm of Moria shall be yours fore ever. Find only news of the thief, whether he still lives and where, and you shall have great reward and lasting friendship from the Lord. Refuse, and things will not seem so well. Do you refuse?"~The Council of Elrond

The dwarves realize the messengers offer from Mordor is full of deception and refuse to help. But it establishes, if Sauron could afford to do it, he would offer some form of "false friendship" instead of spending resources on war and force of arms. When the Western powers show resistance, he uses military force.