I have a fictional world, consisting of a federation of 17 provinces (in blue on the map extract). Currently, it is in the late 1920's. The Dzevogurski and Quidthovitse provinces are on the brink of war. Historically, the province of Ladies Beach was part of Dzevogurski but split away peacefully several years ago for admisitrative reasons. The mountain range running NW-SE formed a natural boundry.
In the region concerned, there are two major railway lines involved in trans-continental transport. The Fyonas River - Kandice Beach line runs through two districts of Dzevogurski. To Quidthovice, this is a major point of 'pain': Their tracks run through their 'rivals' territory.
Also, in the 1890's Quidthovice managed to convince the Kimberley-district government to deny the builders of the Vaenesston-Tannith Beach line access to the 'easy' pass between Kimberley and St. Marias Stone, where the Quidthovice-based railroad company had its tracks laid already. To avoid conflict, the Dzevogurski-Ladies Beach government (sitting in Vaenesston) let this slide.
Now, Quidthovice is trying to 'persuade' the two districts of Kimberley and Murrayville (in red/pink) to join their province. Their current 'parent' (the Dzevogurski province) naturally resists. This time, the Dzevogurski government will fight.
If Kimberley and Murrayville do flip, this will exclave Yadzor.
The districts of Kimberley, Murrayville, Yadzor are mainly cattle ranches, with some fruit (in the mountains) and dairy production. The population is being influeced by both sides.
The question which I'm asking is this: Can two provinces in a federation have a war between themselves, with everybody else staying neutral?
Can you still call it a 'civil war'?
I know that opinion-based questions are frowned upon in this forum, hence this is an optional question: How would this conflict be resolved?