Why suddenly return to Mardis? This is easier to understand. Clearly, the Federation forces in Valan realized that the Titan Elves were not an easy target. On the contrary, staying here longer would only result in greater losses. Therefore, they decided to withdraw and found themselves a good excuse.
In contrast, the Flames Legion's actions were much more righteous. Not only did Mardis accept fifty million Rekart refugees, but he also actively made contact with Rekart. Even the Speaker couldn't fathom what kind of sinister cards the Federation was playing?
Is the Federation trying to annex Rekart? I have to say, it's not an exaggeration to think this way. Rekart in this period is in turmoil. Once, it was the strongest nation in the world, but with the Titan Elves' invasion, Rekart's refugees will be dispersed worldwide.
They might return after the war ends, or settle directly there, or... any possibility.