Alright, the highlights:
*Garrosh readmits Blackrock orcs and former members of the Twilight's Hammer to the Horde. Among them are a number of dark shamans, and Garrosh's new Blackrock bodyguard, Malkorok. Malkorok has anyone who speaks out against Garrosh beaten, arrested, and/or killed.
*Garrosh blows up Theramore with an enormous mana-bomb powered by the Focusing Iris, with the help of a Sunreaver double-agent. Rhonin dies, and Jaina becomes leader of the Kirin Tor. Dalaran does not formally join the war, but is committed to opposing Garrosh.
*Both sides discover Pandaria, fight over it, and recruit some of the natives. In the process they help unleash the sha (though this may have happened regardless).
*The Zandalari, who were once allied with the mogu when they ruled Pandaria twelve thousand years ago, resurrect the greatest mogu emperor of all time: the Thunder King, Lei Shen.
*Two months later Varian and Garrosh arrive in Pandaria, build bases, and start searching for a mogu artifact called the Divine Bell, which can summon the sha. The Alliance finds it first and puts it in Darnassus for safe-keeping. Jaina magically wards it to help keep it out of Garrosh's hands, and the Alliance decides weaponizing the sha is too dangerous.
*The Horde bypasses Jaina's wards and steals the Divine Bell, with the help of another Sunreaver double-agent. Jaina gets pissed and has all the Sunreavers in Dalaran arrested on suspicion of treason. Rommath helps Aethas Sunreaver escape, and the Kirin Tor officially rejoins the Alliance.
*Garrosh rings the bell, but Anduin uses the Harmonic Mallet, an artifact created by the pandaren to counteract the bell's powers. Garrosh tries to kill him, destroying the bell in the process. Anduin barely survives, unbeknownst to Garrosh.
*Garrosh attempts to have Vol'jin assassinated; Vol'jin secretly survives and is nursed back to health by Chen Stormstout.
*The Thunder King and his Zandalari allies prepare to retake Pandaria. The Sunreavers and Kirin Tor send forces to the Isle of Thunder to aid the Shado-Pan in defeating the Thunder King, and to claim some of his power for themselves.
*Wrathion is playing both sides to try and bring a swift end to the war because an unspecified threat is looming on the horizon, and we can't win if we're still at each others' throats. His goals are in Azeroth's best interests, but not necessarily our own.
I think that covers about all the major events up through Patch 5.2. Did I leave anything out?
Edited by Vegdrasil on 5/13/2013 1:13 AM PDT