Orion Senate.. How to get in ? (if you're not there from the beginneng, that is)...

[Proteus_MST]

I often got "Declare Total War on Race x" through the Senate.
Some of them were proposed by myself and some by others (and often seconded by me, if it was a Race I already was at war with). In the End we even successfully issued a bill to declare total War on the New Orions

Aside from this, as bakalov mentioned, there are a lot of beneficial Bills which give you some advantages over Races which are notn in the Senate.