Star Trek Online

To get this achievement u simply have to solve all mission parts in the Yesterday's War Story Arc.

As part of an reorganisation in STO the mission "Temporal Ambassador" was cut out from the -in shadows story arc- (Romulan) and the -vigilance story arc- (Klingon) and was moved to the yesterday's war story arc.

Temporal Ambassador is now the first mission in this arc and its still bugged (August 2020) and can't be completed.

But that's not necessary u only have to start Temporal Ambassador and then u can skip the mission as it doesn't count to the completion of this achievement. Starting the TA mission triggers the 2nd mission what was before the Reorganisation the originate 1st. After u triggered it u can complete all of the other yesterday's war missions and after u have finished the last the achievement should pop instantly.

Good luck!