A campaign cameo clinches it Black Ops and Modern Warfare share a universe. There's a moment in the Cold War campaign where you're invited to attend a meeting with the KGB's inner circle. It's not on Zoom, and you're seated right next to Gorbachev.

As the name suggests, the events of COD: Black Ops Cold War take place during the Cold War. More specifically, the entire campaign occurs in 1981 and sees the return of some characters from the first Black Ops.