Let us also remember that in ancient times and particularly in northern climates, it was a seasonal endeavor. Men (and women, too) couldn't be fighting when there were crops to be harvested for the long winter months.
I should guess this, too, would be relative. While, say, Blackfeet and Nez Perce may have fought isolated skirmishes, they didn't engage in the widespread coordinated attacks that would characterize modern concepts of "war".
good, this got a bit of a discussion going. It came from a statement I saw this weekend on tv, that there had only been 129 days without war in the last 4500 years. I went searching on google to see if that was right, and found that others felt it was 0