Well, 'Gundam War in the Pocket Novel' might be about the struggles and battles within the Gundam universe. Gundam has a vast array of different mobile suits, each with their own capabilities. In this novel, it may show how these mobile suits are deployed in war, the strategies used by the different factions. It might also introduce new characters or expand on the backstories of existing ones, all within the context of a war - torn Gundam - filled world.
The Mobile Suit Gundam manga was indeed the original. It provided the foundation for the subsequent anime series. The anime drew inspiration and storylines from the manga, with some adaptations and expansions to suit the animation medium.
I'm not entirely sure as I haven't read it specifically. But generally, a 'war in the pocket' novel might be about small - scale battles or conflicts that occur in a confined area or among a small group of people during a war.
There were many war cartoons like Gundam Seed:
1 Legend of Galaxy Heroes
2." Mech Suit Gundam 08, Team Ms "
3. Gate of the Fate Stone
Death Note
5. Crown of Sin
6. The Attacking Giant
7 Naruto
8 Sword and Sword God Domain
9 《Fate/Zero》
[10: Metal Alchemist]
These cartoons all involved war and combat elements, but also had profound philosophical and psychological descriptions.
Since I don't know the specific 'war in the pocket novel', I can't say for sure. But usually, there could be soldiers, like a young and inexperienced private who has to grow up fast in the chaos of war.