Diadem is a 1981 board game published by Fantasy Games Unlimited.
Diadem is a game focused on galactic conquest, played on a mapboard divided into 12 hexagon-shaped sub-maps.
[1] David Ladyman reviewed Diadem in The Space Gamer No.
[1] Ladyman commented that "In sum, I won't tell you not to buy Diadem, but I don't recommend it.
There are better-reasoned space warfare games on the market.