Mogu are a race of powerful, magic beings. They have been having conflicts with the pandaren for centuries and their race originated on Pandaria.
In the past, mogu warlords ruled over Pandaria, keeping the pandaren as their slaves. Mogue ruled with a strict no-weapon policy, but the pandaren through diplomacy, tenacity and a from of unarmed combat successfully staged a revolution that deposes the mogu and set up an empire that would last for thousands of years. After millennia of prosperous rule by the pandaren, the Mogu have returned to reclaim thier original homeland of Pandaria. They crave the domain they once held, and, to regain it, they will sweep usurpers and invaders alike into the dust.
Due to extreme strength and size, the mogu constructed an empire primarily based off might in which weak races were dealt with and stronger races, like the mogu themselves ascended to power. Imposing stone monuments and titanic siege engines showed the power of the mogu to the rest of Pandaria. They turned their strength on the smaller, weaker inhabitants of Pandaria, shaping flesh to their whims as they shaped rock. While thy were overthrown in a desperate revolution led by the pandaren, their legacy persists in thousand year-old ruins too immense to collapse.
The mogue had strong connections to the zandalar trolls before the Great Sundering and were close allies during the Pandaria war.
Their current capital, Mogu'Shan Palace is stashed with many secrets about the mogu races' long lost empire, including titan facilities and libraries.
Mogu erected the Great Wall between Townlong Steppes and the Dread Wastes that separated these two region from the rest of Pandaria. The Pandaren saw a need for the wall and so have maintained it since the Mogu race was defeated.
Most races must practice and learn the talent to use magic, but magic is innate to the mogu. Though little is known about mogu magic, they are not mages nor warcloks, but have their own unique role. These roles are known as flesh-shapers and spirit-capture magic. The flesh-shapers were the ones in charge of creating the grummle and saurok races.
Slavery is a major thing in mogu culture. In many ways it is terribly cunning and involved brutal strength. Even though mogu have powerful magic, they perefer slaves to build their massive monuments. branding iron is placed on enslaved humanoids. Forged of iron and imbued with spells of subjugation and pain, the manacles with inward facing spikes were forced onto the enslaved races of the mogu. The blood of mogu is was shed by the bone whip made from the spine of some ancient, humongous creature.
When the mogu were suffering from the lack of slaves, they decided to build animated constructs to battle others. These animated constructs are terracotta warriors that were dormant for far too long.
Little is known about mogu government, they are a meritocracy, where former regime or dynasties must be overpowered or killed.
When the mogu ruled over Pandaria a very long time ago, they were allies to the zandalar trolls that live nearby. The Zandalari assisted them when the pandaren fought against the mogu. Despite being defeated and pushed from the island now called Pandaria, the Zandalari, just like the Mogu, remained in pandaren lore, and slowly turned into the boogeyman of a small child story.
Following the mists disapperance the Zandalari, curious about Pandaria and their mogu allies, they send out their forces to Pandaria. Appearing that they want to re-connect with their ancient allies, the Mogu. It seems they want to assist them in retaking the land away from the Pandaren and bring it under mogu rule again. However the Zandalari seem too desperate to acquire Pandaren territory and appear to have more motives than just helping out their ancient mogu allies.