So are the "threats and intimidation that sometimes get physical" purely due to ice cream sales, or are there illicit goods also being sold from the vans (as per https://en.wikipedia.org/wiki/Glasgow_Ice_Cream_Wars )?
Sometimes vendors will informally buy locations from other vendors.
For example, on a beach, you should expect 2 ice cream vendors to cluster in the exact middle rather than move closer to their respective territories. This video explains it perfectly: https://www.youtube.com/watch?v=jILgxeNBK_8