Trying to understand triangulation

 

I am trying to discover how I am related to person M.  We have no surnames in common but have locations in Cheraws District, South Carolina and Woodville, Mississippi in common. 

I used Gedmatch to find all the kits that match Nikki, person M, and me and then painted chromosome 1 using the new DNA Painter (http://dnapainter.com ) These kits match from 113,140,172 to 159,942,204 or parts thereof.

Each of these people is in common with me and M.  This is the only in-common-with segment and it ranges from 13 to 25 cMgs. All of the data are from GEDMatch.  Part of this area is a common pile-up area, see the gray at the top. 

Using the Triangulation tool at GEdmatch, only B, N, M, and me form a triangulated group. M, I, and C are known cousins but are not in our triangulated group.

Why are there not more people who triangulate? Why would A, C, D, E, F, and G not be part of this group?  What about I, J, K, and L? Would this distribution indicate descent from different couples?

Looks like I have research to do. What steps should I take now?

How are we related Nikki and I?

Over a year ago I was contacted by Nikki in an attempt to discover how we are related.  Nikki and I are not of the same race, she's Black and I'm White.  I've known for a long time that this would eventually happen.  All of my family, both sides, comes from North and South Carolina, through Georgia and into Alabama, Mississippi, Missouri, Louisiana, and Arkansas.  Some of my ancestors owned slaves.  It's a history that is hard to wrap your head around.  You want to respect and think well of your ancestors but the whole institution is hard to accept. 

Nikki and I must be related through slavery.

We have no ancestral names in common but we do have locations.  The Cheraws District of South Carolina and Woodville, Wilkinson, Mississippi. My father's family lived in Woodville and neighboring Amite County, Mississippi and East Feliciana Parish, Louisiana.

This is our journey to discover how we are related.