After carefully analyzing the intent of Eve's words, Marvin had Anna write an answer.
The albatross that had sent the letter was still in White River Valley. It had clearly been ordered by Eve to wait for Marvin's response and bring it back.
In the letter, Marvin expressed his support for the North's forces and also indicated that he would go to Deep Water City as soon as possible.
He didn't speak too much about the details of an alliance, though, because it was just an idea for now. It would be far easier to discuss such things in person.
But Marvin still reminded Eve in the letter that she should be extremely careful of the Gods' forces rising in the North.
Absolute belief was a very frightening thing. In this chaotic world, with the Gods added to the fray, it would be very easy for someone to betray their own ideals and willpower.