The Castor Alliance spanned 80,000 member systems before it collapsed.
The head of state of the Alliance was the Prime Minister of the Castor Alliance and the central legislative branch was the Castor Alliance Parliament, consisting of 1000 representatives called Alliance MPs. The galaxy was divided into 1000 sectors, each one consisting of around 80 systems (some are much larger, others much smaller). Each sector elected their MP every 3 years. The Prime Minister was voted in by Parliament every 10 years.