Liber Necris and Night's Dark Masters both state that Abhorash hated Ushoran because Ushoran was the worst offender in Lahmia in terms of feeding of its population.
According to Liber Necris (I don't think Night's Dark Masters mentions this) the Bloodlines in general took poorly to Ushoran's offer to reside in Strigos because Ushoran had at the time come into possession of Nagash's hand and crown with which he could control them as Nagash had and so viewed his offer as just a trick meant to get them within reach so he could use the crown and hand on them.
Mm, it does not mention it in that context, no. And ironically, it does however mention that Ushoran:
1. Did not care about the exclusivity of the Vampire cult, nor fear Nagash as they did.
2. Replaced worship of Nagash in Strigos when he claimed it with worship of himself and his Bloodline
3. Brought peace and prosperity
4. 'Restored Abhorash's principle of the Vampires only feeding upon criminals and enemy captives, so once again, the people would have nothing to fear from their immortal masters.'
The way Night's Dark Master's frames the ill-fated invitation and response is as follows:
Soon, the kingdom of Strigos was vast and powerful. Ushoran then sent word to his four other brethren, welcoming them to his new Vampire state, where they would be free to feed and live luxuriously, just as they had back in Nehekhara, safe from the hand of Nagash. To Neferata, this seemed yet another insult. Her interloper brother would dare to presume his empire greater than her own (though it certainly was) or that he might ever rule over her. As well, the queen saw at last her chance to get her revenge. She slaughtered Ushoran's messenger and at once spread rumours to the other bloodlines, assuring them that Ushoran either meant to enslave them all, or worse, sell them out to the reborn Nagash. After two hundred years of living with their guilt over abandoning their master and their fear of his revenge, the Vampires had grown bitter and insular. Each bloodline blamed the others for their betrayal and scattering but was prevented from acting on this because of the taboo against harming their own kind. When Neferata gave them a target and a reason to break this pact, the pent-up fury of the other bloodlines exploded in an orgy of violence. They sent mortal armies and Vampire assassins to that kingdom to destroy the interloper once and for all.
So pretty much no mention of the other stuff. Honestly, I'm not sure if he would have put the thing on, lest he be overwhelmed by Nagash's spirit which I think he would not want given his previous open defiance of worship or even fearing Nagash. Though, sources do conflict on Kadon entirely on his wiki page:
Kadon of Strigos Canon Conflicts said:Warhammer Armies: Vampire Counts (7th Edition) and Warhammer Armies: Undead (4th Edition) claim that Kadon founded Mourkain in -1147 IC and was slain with his city in -1020 IC during an Orc Waaagh! lead by Dork Redeye.
Most other sources -- among them Warhammer Armies: Vampire Counts (6th & 8th Editions) and the Liber Necris -- claim that Kadon was killed by Ushoran after the Vampire convinced Kadon that he was one of the gods of the Cult of Nagash, usually around -1020 IC.
The Time of Legends series novel The Master of Mourkain implies instead that Kadon was killed by the Crown of Sorcery for denying its last commands.
With those 'last commands' being to give up the crown to the Crown's desired replacement i.e. Ushoran because Kadon was despite all he'd learned from the Crown growing weak and too rotted to do anything.
So, again accounting for Liber Necris being more specifically an 'in-universe' text and Night's Dark Masters retaining a bit more distance and 3rd Person Semi-Omniscience as an Info-Book built with tables and mechanics and careers and what not...it is certainly a big wiggly.
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Also, ya'll, yeah the Barbarian word history discussion thing, while interesting, should probably stop now, yeah?