I'm not sure specifically as there could be many novels with that title or concept. It might be about a single individual who is extremely powerful and capable, like a hero who can take on an entire army by himself, perhaps in a fictional war or adventure setting.
I'm not sure specifically as I haven't read the whole novel yet, but generally, the main character in such a 'one - man army' themed novel is often a strong - willed and highly skilled individual.
There are some military - themed novels that might fit the bill. For instance, in some of the 'Jack Reacher' novels by Lee Child. Jack Reacher is a loner who often finds himself in situations where he has to take on multiple adversaries alone. He uses his combat skills, intelligence, and physical strength to overcome these challenges. Also, the 'Wolverine' novels in the X - Men universe. Wolverine, with his healing factor and adamantium claws, can be seen as a one - man fighting force against hordes of enemies.
The main character was a modern doctor. After transmigrating, she became the useless eldest daughter of the General's Estate. Because she was killed by someone, the people wanted to kill her.
It could mean that being a 'one man army', someone who tries to do everything alone, often leads to a 'dead end story', like a situation with no good outcome. It might imply that relying solely on oneself without support can be a path to failure or a hopeless situation.