Dominion of Rin
Until 620, the Dominion of Rin was an unremarkable minor polity in central Elthos, along the southern coast. Then Queen Adize Azenya, only recently ascended to the throne, began to drastically expand the royal guard, to the point that it constituted a small army in its own right, though observers noted that the exchequer of Rin could not possibly hope to bear the burden of maintaining such a force in the long term. This was followed by the sudden and vicious invasion of a number of independent duchies between 622 and 627, the pace of the conquest accelerating each time as Rin's soldiers stripped places of their wealth and Adize recruited more and more mercenaries to her cause. In 628, she launched an invasion of the far larger but disunified Realm of Zeth, which crumbled before her invading armies.
Within the imperial court, there was much talk of intervention, but shoddy relations between the Empire and the Realm of Intis to its west, in the wake of the taking of the Duchy of Greenwood by House Salfeld and its allies, meant that the Empire simply had no feasible way to move an army to face Rin. Other larger powers on Elthos declined to intervene either. Rin's strength was such that, besides the Empire, only the Kingdom of Wend or Realm of Westelth would have the power to stand against it alone. Both are far away from Rin though, and the Wendish Crown is focused on internal affairs. The Realm of Westelth, mighty though it is, has not acted beyond its borders for many long years, and when it does so, it is for wholly inscrutable reasons. Most assume it is due to a sign or portent sent by their god, the Prince, who clearly sent no such thing regarding Rin.
Rin completed its conquest of Zeth in early 630. Simultaneous with the invasion of Zeth, and through the course of 631, the Dominion subjugated several more independent duchies and counties. Adize's agents have stripped all the fresh conquests of wealth and she has been open about calling more mercenaries to her banner. Disquieted reports indicate that she is even taking non-humans into her army, whether from the Plains Kingdoms of Salthos, from the badlands of the Red Waste, or even cinderkin shipped from the Scorchlands.
It is not clear where Adize will next turn. It is clear that the more she conquers, the faster she can conquer. Rumour holds that the Lightbearer, the pontiff of the Church of Siegfried's Light and ruler of the Divine Assembly, is likely to call for an armed pilgrimage to scour Rin of all evil, though success in such an undertaking seems improbable - the Divine Assembly is a small realm, and the Lightbearer would be heavily reliant on members of the church from elsewhere participating. Other polities in central Elthos are increasingly alarmed, but beyond strengthening border garrisons, have made no move. The Confederation of the Purple Coast has been at peace for many years and has only lately put its money towards recruiting soldiers, which may be too late to stop Rin from plundering its deep coffers. The king of Intis, on the border of the Empire, has instructed his vassals to prepare for war, but by now, Rin's strength dwarfs that of Intis.
As for the Empire? The matter remains a major talking point in the imperial court, but no one approach is agreed on.