This is a tough one to figure out. The immediate subject appears to be a family reunion, with three or four generations present. Nothing terribly unusual about that as a subject for a late 1800s photograph.
It's the venue that has me puzzled. They appear to be staying in tents, and the expressions of the people at the far right, looking on, are of concern or aprehension. On the back is a photographer's stamp, "Martin, Photographer. Ottawa, Kansas."