Market division

Dividing territories (also market division) is an agreement by two companies to stay out of each other's way and reduce competition in the agreed-upon territories. The process known as geographic market allocation is one of several anti-competitive practices outlawed under United States antitrust laws. The term is generally understood to include dividing customers as well.

For example, in 1984, FMC Corp. and Asahi Chemical agreed to divide territories for the sale of microcrystalline cellulose, and later FMC attempted to eliminate all vestiges of competition by inviting smaller rivals also to collude.

...
Wikipedia