Here are some of the very, very broad strokes of galactic history. It’s very sparse, so think of this more as a bunch of eras for writing more specific stories in rather than actual galactic history. Not to mention, there’s plenty of gaps.
~100,000 BBY - The First Beings leave their home planet, the identity of which is lost to time. They begin to colonize the galaxy through conventional space travel. Because conventional space travel is so slow, each star system is basically entirely isolated, and so the First Beings evolve into the many millions of beings of the galaxy.
~30,000 BBY - Very early Force users learn to create portals between star systems. Most star systems are not accessible through portals, and the ones that are only link to a small handful of other star systems, but this is enough to create a few galaxy-spanning portal webs, allowing for the first galaxy-spanning Empires and the beginning of Galactic Civilization. Early rulers of these galaxy-spanning Empires are despotic Kings trained in the Dark Side of the Force.
~25,000 BBY - Slave Rebellions in one of the web Empires, assisted by the first Jedi, begin winning victories. Eventually they take full control, founding the Galactic Republic. It’ll exist in many different forms, but won’t fall for over a thousand generations. The Jedi Oath is written.
~4,000 BBY - Hyperspace travel is invented, opening up the entire galaxy to civilization. This embroils the Republic in two conflicts: One with the Mandalorians, who had their own web Empire, and one with a new group called the Sith, a xenophobic group of Dark Side Force Users who want to eradicate the galaxy of the alien species newly introduced to galactic civilization. The Republic ends up defeating the two of them, casting them to hide in the dark shadows of the galaxy.
~1,000 BBY - The galaxy experiences centuries of peace and prosperity after rebuilding from some conflict.
100~20 BBY - The galaxy undergoes a cultural revolution, turning away from the spiritual, and toward the material. Tons of new technologies are invented, but also horrifying weapons of war. The Jedi’s numbers dwindle over decades until Darth Vader finally finishes them off, but in this time, the old foe of both the Mandalorians and the Sith return. The Republic finally falls around 30~20 BBY, and the Galactic Empire rises from its ashes.
4 ABY - The Emperor dies. Who knows what happens next?
Because there’s been a bit of a reset, I’m leaving out some of the eras/events that might not be brought back. Unfortunately, the Viral Wars, something I thought was really cool, is probably not gonna stay. Alas.