that prologue tells of the Tiste Andii and Tiste Edur fighting a big battle together against the K'Chain Che'Malle, having just entered the Malazan World from their warren. At the end of the battle, they are victorious - and then Scabandari Bloodeye has his Edur turn on the Andii and massacre them, while Silchas Ruin is imprisoned in an Azath House, and Gothos (or possibly some other Jaghut) buries the whole thing in ice.

So that all happened on the continent that would become Lether, which is why Lether is the home of all the Tiste Edur and several small populations of surviving Tiste Andii - and why they have those ice fields.