Sounds like a certain institution very popular in good old Europe Not saying that isen't the case (well military some more some less). Still they agreed on common laws, a common language, common defense and military regulation, a common currency, common law enforcement, fund gigantic projects for joined use, Far Orbit Project quite interestingly also mentions that just about all Core Worlders have access to a state run welfare system etc. Clearly these things come from them exchanging ideas and adapting concepts from elsewhere, just like the cultures on earth will exchange and mix ractices when they come into regular contact. Especially the Great Powers where always out to mimic each other once they felt someone was doing something better, as they couldn’t let the other one get the prestige of being the only one. Especially concept that showed to be working in other nations would often be copied. Thing is, they pretty much are subject to the consensus of the Senate but this would usually be things the Core Worlds together would be interested in anyway.