The Inhumans are a superhuman race created from genetically altered humans by the Kree. The Inhumans went to form their own society and lived in seclusion from humanity. The Inhumans are led by Black Bolt and his Royal Family.
Over a thousand years ago, the Kree visited Earth and observed humanity as the potential for a race of superhuman shock-troops, to use against their mortal enemies, the Skrulls, and, in time, against the people of Krypton. Over five centuries, the Kree experimented on a group of humans, until those humans rebelled, and drove their former masters away. It was at the exact same time that the Kree and Skrulls engaged in a space battle above Earth. The battlefield was interrupted by Kon-Lir's Speeder and forcing both sides to immediately attack the Kryptonian vessel.
Although the Speeder was shot down, the Kree and Skrulls suffered major losses and were forced to withdraw from Earth. The experimented humans then built Attilan from the remnants of the Kree outposts on Earth, and called themselves the Inhumans, to forever remember what their ancestors had endured and survived.
Over time, Earth's pollution became hazardous to the Inhumans and were forced to relocate themselves and their city to the planet's moon. Since then the Inhumans remained in seclusion and their existence are only aware by S.H.I.E.L.D., whom maintains a neutral diplomatic relationship with Attilan.