Gandalf, blood of hobbits on his hands?

[Andsigil]

Originally Posted by The Might

There you are wrong, since I would not be considering diplomacy with Sauron, but with those supporting him, the Men of Khand and Harad and further into the east.

I believe they could have been reasoned with and brought on the good side.
Now you may argue that this was attempted and failed - with the Ithryn Luin setting off to the east and possibly having founded magic cults around themselves and with Gandalf having also went a bit further South (not that far) where he gained the name Incanus.

But I do not believe that all was done that could have been done. Gondor's insecurity of how to handle the southern neighbours and their seeming unwilligness to initiate any true diplomatic talks is what brought the Easterlings and the Southrons closer to Sauron.

First of all, we know they could be reasoned with, we see that after the war when peace is made with the people of the south and the east.

But unfortunately, we hear of no such attempts by kings like Romendacil or Hyarmendacil, they just conquer, but don't seem to try and win over the population.

I believe that had these people received better treatment, had Gondor invested more in helping these people they conquered, improving their lives for the better, then they would have been a lot more resistant to supporting Sauron.

It's possible, I'll grant you. But I doubt it. As I mentioned before, Sauron proved that blockading him doesn't work. He only has to wait a few generations for the pitiful little mortals to die out and change their policies. That's assuming he hasn't patiently subverted them outright. Sure, Gondor could have befriended the men of Khand and Harad... for the time being. But what would happen after, say, 500 years, which is a meager amount of time to Sauron? Look at how many times over the last 200 years alliances and oppositions have changed in Europe between the UK, France, Spain, Germany (in its various incarnations), Russia, and Turkey. Every one of them has been both ally and enemy of the other at some point.

Sauron is immortal. And bent on conquering Middle Earth. And evil (Let's keep it at that. I'm not into moral relativism and I'm utterly unconcerned with what things look like from the points of view of Sauron or the various orc races). You can't blockade or defend against him forever, otherwise he finds a way around you. Eventually you have to take the offensive against him.