The Galactic Union (GU) is a Galaxy-wide organisation. It is a coalition of many galactic empires, and can very well be compared to the European Union in our own world. It is no where near as powerful and influential as an autonomous entity as the Galactic Republic in Star Wars, however.
In the year 8 PTX (Pre-treaty of Xcaolon, when the Galactic Union was formed), an enormous Grox Offense Force left the Core Blockade Zone and started cutting a bloody, burning path through the galaxy. Civil wars were already raging throughout the galaxy and the Grox conquered world after world, system after system, and sub-sector after sub-sector. One year into the Grox conquest, an emergency summit was held on Turun XI, organised by the Romenaz Corporation, the Senonian Federation and the Zathodox Monarchy, three of the Galaxy's largest power blocks at the time.