https://www.polygon.com/2018/10/12/17969502/call-of-duty-black-ops-4-league-play-ranked-system

When Call of Duty: Black Ops 4 was first announced, one of the standout features that developer Treyarch announced was the return of League Play, a popular competitive feature from Black Ops 2.

League Play doesn’t have much of an analogue in traditional console shooters; instead it finds its roots in more competitively-focused PC games like League of Legends or Counter-Strike: Global Offensive. The return of a more focused ranked mode in Black Ops 4 was a sign of Treyarch’s bigger plan to create a competitive ecosystem that exists entirely inside Black Ops 4 called the World League Hub.