Alright you bitches, how many times do I gotta say this? This goddamn game is like a
Fantasy Cold War. There is no official war between the Horde and the Alliance, and all fighting is unsanctioned by either Stormwind, IronForge, Darnassus, or Orgrimmar. Let's go over a few points shall we?
Kalimdor
Jaine Proudmoore, heir to the Kul Tiras naval forcesse, is forced to choose. The orcs are setting up a home in Durotar and her father, being a staunch opposer to the Horde, attempts a military action to keep them from from doing so. As Jaine fought alongside the orcs in the Third War, she knows they are not bloodthirsty monsters anymore. The choice is to aid her own father in his personal war against the orcs and Darkspear Trolls or fight against him to support her new allies. She chose the latter and aided the orcs in defeating Proudmoore. The ruins in Durotar are proof of this. In exhcange for her aid Thrall lets Jaine return to Theramore and allowing them sanction against official Horde threats. Theramore was made after the Third War for the Alliance who were fighting to save Azeroth from the Burning Legion. And Thrall allows the humans to live there in gratitude to Jaine for her help.
Ashenvale
The original Night Elf homeland is currently being disputed unofficially by the Horde and Alliance. The orcs are there to construct towns and expand their holdings. But the Night Elves wish to re-settle in their former homeland since the Third War. It's of course contested which mean neither side as enough military force to secure it, so adventurers like the players themselves are employed unofficially to help.
Stonetalon Mountains
This area is much like Ashenvale, with different people. The goblin Venture Co. settled into the area to deforest the forests for business, This did not bode well with the children of Cenarius, whom fell defending Azeroth against the Burning Legion. Tauren and Night Elfe druids set aside differences to aid in restoring Stonetalon to it's natural glory. The children of Cenarius fight against Venture Co. and the creatures drawn in from the burning of the Charred Vale and the Taurens fight against their fallen brothers the Grimtotem who have ravaged the Taurens living here.
Current Affairs
The Alliance at present is weakened. All available soldiers are called off to fight in a war without reason or cause right now, leaving Stormwind and Ironforge without enough men to defend their people. The humans fight against the Defia Brotherhood and later the Syndicate, the Dwarves and Gnomes attempting to stop the Darkiron dwarf plots to break their kingdom and subvert their cause as well as the troggs who erupted out of the ground while the dwarves attempt to use archealogy to find their heritage.
In Lordaeron the Forsaken attempt to make a place for themselves while doing battle with the corrupt humans of the Scarlet Crusade as well as the Scourge who is still left when Arthas (as the new Lich King) fled to Northrend to lick his wounds. They also attempt to use alchemical research, they tell their Horde allies the falsehood that they seek to find a way to cure their undeath and restore themselves to something more than the Scourge but they are actually attempting to make an ultimate plague with which to wipe the humans from their lands. And possibly even all living things to create their own undead utopia. They also fight the humans in Hillsbrad and Alterac, who being cut off from Stormwind so long, fight simply to survive.
Darnassus fights those who try to encroach on their lands, but the orcs are least of their worries. With Malfurion, the rightful ruler, lost in the Emerald Dream the Priestess Tyrande and one of Malfurion's druid companions to tend to the civli affairs. Strange cults are spawning in their borders and the wildlife is being mutated by some unknown force after they made a new and unblessing world tree.
And Thrall attempts to settle in and found a stable nation but old cults still loyal to the Burning Legion attempt to subvert his goals. All the while keeping heads cool over the fighting occuring everywhere.
And the Tauren battle the Venture Co. mining and foresting operations in their own lands as well as aid their orcish allies and dealing with the Grimtotems.
It's all a big mess you can read, but by now means a official or all out
war.
If you want you can read
The History of Warcraft.l