https://imgur.com/a/aFzfnXU
In the first map we can see the grand expanse of four troll empires. We can also see what land the Dark Trolls migrated to.
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In the first image, we see how Cenarius guided the night elves as a people. How they embraced nature and are basically the perfect hippies for “many centuries.” No wars.
In time night elves discovered that the Elune-Blessed Titan Blood that digivolved them from trolls into night elves could give them super magic. And so, the Highborn evolve and with them cometh Queen Azshara, Lord of Dabbing.
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Queen Azshara held the most coveted traits of her people. The lowborne adored her, even if they hated the highborne. It is in this time that the nelven empire begins expanding its borders via PAX NELFANA and taking lands as their own. This happens before Troll combat is ever mentioned.
During this moment, Cenarius watched with growing unease as her empire expanded. Lowborne still loved nature, but they agreed with Azshara: She believed her race superior to all others. Her people, including the lowborne, were rife with xenophobia.
Map 2 Before we even read about troll combat, we’re shown Azshara’s designs on the world: It is her world, and trolls are, at best, guests upon it. They were intent on taking land, and were taking land, and the trolls reacted to invasion into their homelands.
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The first mention of “troll aggression” comes after PAX NELFANA initiates. Azshara didn’t care. She charges the Zandalari with policing all other trolls to stop them from invading “nelven territory” (see: MAPS 1 & 2). The Zandalari agree purely because they know they cannot survive PAX NELFANA if they decline: they will be killed.
With the Zandalari enslaved to police the other trolls and keep them in line, Azshara continued expanding her empire.