The vast majority of the (inhabited) planets join the Council and agree on standardisation, space law and peaceful negotiation of differences.
A coalition of extra-galactic forces, known as The Realms suddenly attacks. After two years of strife and destruction they are finally defeated by the Intergalactic Council's Coalition Forces. However, many planets and sectors are lost forever, most notably the Denorian Kingdoms (aka The Astral Empire).
The last battle of the War of the Realms where the elite rearguard forces of The Realms were annihilated loosing their last foothold. The battle is infamous for its viciousness as there are few if any confirmed survivors.
The Intergalactic Council reconvenes and decides on its new structure, the fate of war-ravaged planets, refugees etc. No matter their efforts however a period of isolationism sets and intergalactic relations diminish. Political events change many planets, empires and federations fade.
A revolution in the kingdom of @Radonia in the Old Realms sector results in Denorian refugee forces coming to power.
After years of isolation and recession, intergalactic trade and relations begin to flourish again, new space stations are built and the Intergalactic Council gains momentum again.
The planets that have fallen under Denorian leadership are united in The (new) Astral Empire and lay their claim to be recognised as empire and receive their share of resources thus sparking the Colonial Wars.
The three year conflict that practically brought the end of independent planets and the demise of the power of the Intergalactic Council.
The only instance in which two empires clashed during the Colonial Wars. Ended with defeat of the Amazons and the de facto recognition of the Astral Empire. Practically marked the end of the Colonial Wars.
Officially ending the Colonial Wars and establishing the present status quo known as Pax Imperialis.