Score

The total score (and thus number of stars) is directly influenced by the following (ordered by most to least impactful):

Total number of days

Completing all goals before 200 days will yield a very high score. Above 1000 days, the game will apply a score penalty.

Population

Each population level will add around 100 points to the total score.

Morale

Positive morale can provide a score bonus.

Authority

Higher final Authority increases score. Impact is secondary to Days/Population.

Difficulty

Higher difficulties allow for higher potential scores.

Formula

The exact calculation is not yet fully reverse-engineered. Key components appear to be:

• A base value heavily modified by Days Taken.
• Additive points from final Population and Authority.
• A percentage bonus from final Morale.