I have a fondness for the Moties from The Mote in God's Eye and it's sequel, The Griping Hand. They are a hierarchical society with a biological necessity to reproduce or die. This leads to incredible population pressure and resulting societal collapse. Being "trapped" in one solar system they became the ultimate fatalists, believing that the "Cycles" of society would be repeated eternally until/unless the Moties finally wiped themselves out completely. Second in line would be the Kzin, the universe's poorest diplomats.