Ulmat Thondr was a peninsula in the far south of the continent of Azeroth. It was under watch by members of the Order of Tirisfal. During the First War, it was quiet there and there were no signs of orcs, though there was a rise in the number of jungle trolls. A new comet was said to be visible along the southern horizon.
As it was located in the far southern edge of Azeroth, it would currently be in Stranglethorn Vale.
Stranglethorn Vale recton?
It is also higly possible that Ulmat Thondr was actually what we know by the name of Stranglethorn Vale, but Blizzard later retconned and slightly altered it, since Cape of Stranglethorn is a peninsula.