THE FORLORN HOPE started in 1980 with a phone call from Susan Allison, who had just taken over as SF editor of Ace Books after Jim Baen left. Ace hired her away from Pocket Books, but earlier she'd been Jim's assistant and knew both his methods and his authors, me included.
Military books--fiction and non-fiction--were selling very well at the time. All the divisions of Ace Books had been directed to start military series. Hammer's Slammers had been very successful for Ace (at the time, I had no idea how successful) so Susan came to me with a proposal:
I would write a military SF novel, introducing characters and a milieu. Later volumes would be farmed out to other writers. There was no suggestion of me plotting novels for others to write--that whole business started years later--but I had reason to expect that I'd be paid a considerably larger advance than I'd gotten previously.
I started writing the book without waiting for Ace and my agent to work out the contract details. I used Xenophon's Anabasis--the March Upcountry--as a model for the opening situation but based the remainder of the milieu more on the Thirty Years War. I had a good time writing the book while waiting for a contract.
The contract didn't come. Ace was in severe financial straits, facing bankruptcy. I finished the book and light dawned: Putnams had bought Ace, providing the SF line with real financial backing for the first time in years. Obviously there were going to be delays while the new owners looked over projects, but I thought I had reasonable hope of getting perhaps as much as $20K for the book.
Ace offered $7,500--less than I had gotten from Tor for Skyripper. I went ballistic. When Jim Baen heard that I had a completed military SF novel in hand, he immediately offered $15K for it. My agent felt that we owed Ace the chance to raise their low-ball offer (so far as I was concerned, if I never heard about Ace again in my life it was too soon. I was very frightened of my new status as a person without a regular paycheck, and as a result I was silly about a lot of things). Ace raised their offer to $12.5K, still below what Tor had on the table, and I gleefully took Tor's offer.
I like The Forlorn Hope, but I've never felt a desire to write a sequel to it. The book was meant to have sequels, but I never from the first intended to write them; I'd ended it at the point that satisfied me.
Xenophon, I think, would have understood.