The reality of Earth-919 has gone through twelve different incarnations, all triggered by different instances of multiversal renewal, which constitutes in the destruction and re-creation of everything there is.
Little is known of most of Earth-919's incarnations. The second is said to have been a dark cosmos of deep magic, and the ninth was the universe where the paradise-like planet of Taa existed. When the sixth incarnation was destroyed, it was eventually reborn as a consequence of the Big Bang.
This eighth incarnation is the most widely known of them all, where the Earth existed, protected by heroes like the Avengers and the Fantastic Four. The seventh iteration of Earth-616 suffered from an early death as a consequence of the multiversal phenomena known as the incursions. The intervention of Mister Fantastic in its rebirth caused the eighth incarnation to be a completely new version. Because of the abnormal nature of the most recent death and rebirth of the Multiverse, some of the Abstract Entities argue that the current incarnation is still the seventh, while others claim it is the eighth indeed.
Earth-919 has all the features of our reality: same countries, same personalities (politicians, movie stars, presidents, etc.), same historical events (Trojan War, World Wars, 9/11, etc.), and so on. However, it also features distinct ones, such as countries like Wakanda or Genosha, and organizations like the espionage agency S.H.I.E.L.D. and its main enemy, Hydra. Earth-919 is the mainstream continuity of the Marvel multiverse (Earth-616) and where most of Marvel's comics take place. The difference is, everyone from Earth-616 has long since passed as if their time ended prior to Earth-919 taking shape.