We don't know exactly what the year is, but three hundred years ago legend tells us that there was a celestial catastrophe ending an unknown war. Terra, long ago known as Earth, was destroyed leaving a hole in space and time. Fortunately, we had already terraformed Mars and Venus years before this and humanity, as a species, survived.
Our technology waned without the support of Terra. We were able to maintain some of the old technologies, but many technologies were either in the hands of monopolist groups or completely lost. On top of this a great computer virus wiped database and backups nearly clean removing all but printed accounts of history. This caused a dark age that lasted more than a century.
There is no magical warp drive or hyperspacial interstellar travel. We're limited by the speed of light in both communication and in travel, so most of humanity is still located near the core of the system. We were stuck with fusion propulsion drives which were difficult to maintain and expensive to fuel. One day Neptunians reintroduced themselves to the rest of Sol and sold reactionless gravity drives which make space travel fairly cheap and quite safe. Almost instantly a golden age of trade blossomed.
There is a cold war between Mars and Venus, which occasionally turns hot briefly. No one expects a outright full war as human life is more precious now than at any point of history or legend.
As far as we know there has been no contact with intelligent alien life, but we have created our own companions. Many centuries ago, well before the loss of Terra, many animal species were gene-spliced with humans and we have stable colonies of hybrids who struggle for both independence and equal rights. There are also advocates for giving intelligent machines equal right as well but, artificial intelligence is tightly regulated due to the legend of a great war between machines and humans sometime far before the loss of Terra.