It's even worse. They weren't asked to trade. They were obligated to trade, because they had a trade treaty with the Horde. Which they broke over Wrathgate already after WotLK, so about a year after Wrathgate happened. And the best part of that? After WotLK, the factions were attempting a peace process to end a war that the Alliance also started. Which they did also over Wrathgate. And breaking a trade treaty over the same event you already declared a war over and were trying to end by the time of the said trade treaty breaking is kinda psychotic.
But the Night Elves didn't start the war. Varian did in Undercity. Night Elves only took a dump on the peace process (and even then they had huge help from Varian as well).
One must be a particularly brilliant specimen of an Alliance genius to accuse @
Chief Bennett of whitewashing Sylvanas.
Also, there was no betrayal of the Alliance at the Broken Shore, from any perspective. The Horde retreated immediately after the spaceships stopped shooting at them. The spaceships started shooting at them immediately after they warped in on the battlefield. The Horde clearly retreated because being fired at by
spaceships broke their ranks. Alliance could see the spaceships warping in and firing at the Horde, they are visible from the Horde position. As such, Alliance had the information necessary to get to the conclusion that the Horde withdrew because of the spaceships.
Furthermore, once the Alliance got onto their gunship, they had the aerial view of the battlefield and they could see the Horde side was swarming with demons, because there were active portals on the Horde side.
Finally, just using basic logic, the Horde wants to live. Sylvanas more than anyone else. They had no logical reason to risk dooming the world by deliberately letting the Legion win just to fuck the Alliance over.
And given that the Alliance also retreated because of the Horde's retreat, once the Alliance learned that 1. Broken Shore was unwinnable without Pillars of Creation and 2. Broken Shore was a trap sprung by Detheroc who infiltrated the Alliance, the Alliance should kiss the Horde's ass for indirectly saving them by forcing them to retreat as well rather than staying in an unwinnable battle (on which Gul'dan dropped a Fel Reaver which would incinerate the Alliance if they weren't on the gunship).
And Genn learned about Eyir at the very end of Stormheim. He attacked Sylvanas at the very start of Stormheim. Try to figure out the chronology on your own.