The Captain Lewis Nixon Band of Brothers character was demoted despite being shown to be an intelligent and capable officer. He featured as one of the main characters in the series, and Band of Brothers episode 9, "Why We Fight," focused entirely on his story. It was revealed in this episode that not only was he demoted from Regimental S-2 to Battalion S-3, but also that his wife was divorcing him and taking everything. The horrors of war and his wife's letter can explain some of his motivations behind the reason he was demoted but by the end of the episode, why they fought was made clear.

https://screenrant.com/band-of-brothers-nixon-demotion-explained/