The Starways Congress has always seemed a bit weak to me- there is no way to enforce their policies without taking decades, as demonstrated in Speaker for the Dead. It was formed sometime after colonization began, so presumably between Ender in Exile and Speaker for the Dead.
What was the thought process behind it? If all of these thousands of colonies are different cultures and nations of people essentially not capable of making war with each other, what is the point of having a governing body? Instant communication is possible through the ansible, but that can only be used to threaten and not physically solve problems. If two planets were to declare war on eachother thirty years away from the governing body, what could the Starways Congress do to stop it? What gives them the right and power to rule?
Since all planets must be self-sustaining, they're likely very autonomous. The only functional part of the Starways Congress should be something like the interstate commerce clause of the US constitution. However, it seems like it's got much more power than that.
Presumably, most planets get a representative in Congress. Why would they meet in person if it could take decades to reach the "capital"? Why wouldn't they just transmit via ansible?