Remember that different sects of Islam often do not view other Islamic sects as “believers” but rather view them as “unbelievers”, or more often (and worse) as apostates.
So, to us westerners, it looks like Muslims fighting Muslims, but to them, it looks like the “faithful” warring with the “unbelievers or apostates”.
True that. Sunni vs. Shia, Arabs vs. Blacks, etc.