History:

During the Fourth Crusade, seven knights in service to the Seven Houses (seven royal families) participated in the sack of Constantinople. These knights were needed to keep the Wesen in line that made up the brunt of the Royals' Army. The knights brought back a treasure from Constantinople so powerful, that they feared it coming into the possession of their masters. They hid the treasure and created map in Seven parts.

The Verrat:

The Verrat (ver-RAAT; Germ. "betrayal") is a powerful Wesen organisation established in 1945 that serves the seven royal houses (the Seven Houses) whose goal is to maintain stability within the Wesen world. 

The Keys:

The seven parts of the map created by the seven knights were then engraved onto seven bronze keys, and each knight took one of these keys to hand down the grimm family and keep it from the royals. However, the Royal families did find out and after six hundred years of considerable bloodshed, have obtained four of the keys. Nick Burkhardt (see chapter three) owns two keys, one belonging to his own family and one given to him by another grimm. However, the location of one key is yet to be discovered.

It is thought the treasure is hidden some where around the black forest in Germany, but just whereabouts is not yet known, as obviously all seven keys are needed.

One of the seven keys, belonging to Nicholas Burkhardt. Each side is engraved with a part of the map, and when dipped in ink and pressed on paper, pictures a clearer image. It is presumed the key also helps unlock the treasure.

The Resistance:

The Laufer (LOW-far) or Resistance is a movement of mostly Wesen who oppose the Verrat and the rule of the Royal Families. 

The Laufer are also hostile to the Grimms due to the latter's tendency to work as mercenaries for the Seven Royal Houses  and the Verrat, under the belief that they share the same goal of enforcing order among the Wesen. The members are unaware of the fact that the Grimms and the Verrat are only allies by convenience.

The members of the Resistance are mainly made up of Wesen, though there are humans and a few Grimms.

History of the Laufer (World Wars):

Led by Danilo Llic, who was some sort of weasel-like wesen, a Serbian group of rebels known as the Black Hand was responsible for the assassination of Archduke Franz Ferdinand of Austria. This led to both World War I and the fall of the Austro-Hungarian Empire.

It is unknown when the Laufer was first founded, but the Grimms first became aware of them during the Second World War, when the Verrat infiltrated the Spanish army and monarchy during Franco's regime and began mass executions of Wesen suspected of being in the Resistance.