The Promethean Empire had attempted to invade Terra once before, but their plans were foiled by the Grand Alliance, Compact, and Coalition, who all evicted the Promethean forces from the system. The Prometheans, having recovered from their defeat so many years ago, now set out to exact revenge on the weakened Coalition and Compact, as well as Humanity. A small fleet of twelve ships entered the Sol system in January of 1973 and set up offensive positions near Venus.