Nazgul At Pelennor

[Voralphion]

why WAS Sauron battling on different fronts at the same time?

I thought of this as well when I was typing my previous post. There seemed to be no reason for Sauron to be fighting fronts at Lorien and Dale as well, unless it was for the specific reason of stopping extra aid that might come from the men of Dale, the Dwarves of Erebor and from the elves of Lorien and Mirkwood. But, knowing the lack of enthusiasm the elves had in joining with men and the distance from Dale to Gondor, this seems unlikely that they would send aid.
Sauron's main purpose was regaining the ring, that he thought was at Minas Tirith or was going there, (as this is what he would have done, and seemed the most logical place for the ring) and so it seems stupid on the part of Sauron to waste his time attacking Lorien and Dale when he could have easily destroyed them after the ring was found.

I think that the reason Sauron attacked Dale and Lorien was because Tolkien wanted to show that all of middle earth was at war, not just Gondor.