As stated in the Evelopedia:
EVE is a massive multiplayer online game (MMOG) set in a science-fiction based, persistent world. Players take the role of spaceship pilots seeking fame, fortune, and adventure in a huge, complex, exciting, and sometimes hostile galaxy.
The game is set in part of the universe that is currently unknown. The game world consists of about 5,000 solar systems. When EVE was released in May 2003, about half of these systems were available for exploration, enabling players to more easily establish “hot spots” – centralized locations for trade, commerce and combat – based on their activities. As the population in EVE grows, more systems are made available to avoid overcrowding.
EVE has a rich history and unique storyline created specifically for the game. The history, or “prime fiction,” details the discovery of a natural wormhole that lead into an uncharted area of the universe. Gates were created to enable explorers to pass back and forth between the old and new worlds until the portal closed suddenly and violently, leaving the settlers cut off from the civilization of Earth’s galaxy.
Of the settlers that survived the hardship of this harsh environment, five nations rose to power, each taking on its own unique appearance, political and religious views, strengths and weaknesses. These five nations dictate the balance of power. After generations of war and strife, players enter EVE during a time when the general political situation is one of peace, albeit a strained and sometimes fragile one, between the empires.