Random setting idea. Expansion of a post I made with image a while ago.
The galaxy is, from a FTL astrography perspective, divided into two brad regions. The main, wider galaxy is everything but the second smaller region - a single stretch of space a thousand light years wide by 50 thousand light years long from core to rim, with Earth luckily enough to be in the exact center of. Within this zone, the Void Corridor, FTL travel is normal as it is outside the Corridor, what is blocked is easy travel from outside to inside, except from a few special easily missed plans.
The Void Corridor isn't natural, it is an ancient creation of a now extinct species some hundred thousand years ago. Why they built it is unknown for all that remains of said species are ruins. That said a lot of theories do exist.
The point if this is that species inside the Corridor are safe from the going one outside the Corridor. Including the presence of horibble nightmarish species that occasionally crop up to destroy all life every 50,000 years.
Humanity is inside the Corridor, as mentioned. In fact the Sol System is exactly half way both spinward-antispinward and coreward-rimward. Even more lucky is the fact that while other sapient species exist Humanity and it's selfmade kin (the uplifted and bioengineered mutant animal Gaians and the fully sapient AI Anima, plus the augmented and human subraces) are the most technologically advanced in the present day.
Human history can be broken up into four rough periods. Now to 2100, Earth progresses, wars occur, technology is developed. In 2096 the FTL engine is developed which leads to the start of interstellar colonization. This first version is slow, risky, high maintenance, and expensive but it works - leading to coloni station to the 59 systems around Sol, the Spacer Systems. Between 2100 and 2200, Earth dominates the governments of the Spacer Systems. In 2194 this changes when war occurs and the technological advances Spacers push Earth forces back to Sol then Earth itself. Treaties are signed restricting what Earth can do outside it's system. 2200 to 2500, the Spacer Era. The Spacer worlds develop technologically and gain focus in culture. Thdy don't, on the other hand explore much beyond the original sector. It is during this time that the augmented, the Gaians, and the Anima are created, and wars are fought. In 2486, Earth is united by an immortal man who goes on to record human unity - creating the Terran Empire by 2500.
It is now some time later, actual date not decided, and the Terran Empire has grown to encompass tens of thousands of light years of space and mostky peacefully absorbed some eight other species. Not that imperial history is all that peaceful, as wars have definetly occurred.
My thinking is that near the start a discovery is made on a bridge of systems leading to a space outside the Void Corridor. Which is something that would change the game as the Empire meets others equal in technology to it for the first time.
What that Other is I leave up to GM decision. Ideas could be a Mass Effect like galaxy with the Void Corridor being there to stop the Reapers.
Just wanted to share this nifty idea I had.
Oh. As a note. My version of FTL is called the Jump Engine and exists on large ships in a Drive version and in space gates in a, well, Gate version. Both lead to a sort of artificial wormhole highway system ships fly down at speeds varying based on engine rating. :)