let us see authentic narrations in this regard

we find bukhari and muslim writing

” سِباب الْمُسْلِمِ فُسُوقٌ وَقِتَالُهُ كُفْرٌ ”

insulting/reviling a muslim is sin and fighting him is kufr/disbelief

[online link bukhari]
[online link muslim]

similarly we see holy prophet forbade sahaba not to fight each other, and termed it kufr

both, bukhari and muslim wrote

” لَا تَرْجِعُوا بَعْدِي كُفَّارًا يَضْرِبُ بَعْضُكُمْ رِقَابَ بَعْضٍ ”

: Do not return to unbelief after me by striking the necks of one another

[online link bukhari]
[online link muslim]
[online link english translation of muslim]

so what about those who fought imam ali (a.s)?

or let us make it more easy, what about those sahaba who fought those wars?