Balance of Power: The 1990 Edition was a special edition release of Balance of Power sometimes referred to as Balance of Power II). It was released simultaneously on five platforms in 1989 after the original achieved many sales.
The 1990 edition adds more countries, advisors to help out the player, a new "multi-polar" level that allows countries to generate events of their own (such as declaring war on other countries), and a few miscellaneous features. However, with the ending of the Cold War, interest declined, and there have been no further follow-ups or clones.
Source: Wikipedia, "Balance of Power (video game)", available under the CC-BY-SA License.