Answer:
Most other wars calls for a nation (and his/her allies) declaring war or special military operation against another nation (and his/her allies). These can be broken down to different types of wars as well, but typically it is against foreign adversaries.
What makes a civil war different from other wars, is that both oppositional sides of the war are groups (or factions) within the same country. This means that all of them were citizens at one point, in which the disgruntled group breaks away politically to form their own nation to continue to strive for what they want, which the previous majority would not give them. In essence, each side is fighting their own countrymen.