Silhouette was formed around the Mid-21st Century when it was discovered that the French Government was secretly under the control of Majestic-12 and was a puppet government for the real rulers of both France and Europe. Things soon got worse when it was also revealed that the United Nations with cooperation with the French Government, were secretly keeping poorer citizens from getting the needed cure for the Gray Death and soon led to the formation of Silhouette.
Events of Deus Ex
During the events of Deus Ex, Silhouette is one of the various terrorist organizations in the world and are currently participating in an active armed insurgency in France against the MJ12 backed French government. It has formed an alliance with the National Secessionist Forces and X-51, both organizations who have the same goals of seeking to overthrow the MJ12 regime in the United States. Much like the NSF, it is up to the player's decision if they will be allies with both them and Silhouette if they discover the MJ12 control of UNATCO and is true intensions. If the player doesn't discover UNATCO's true intensions, both groups are antagonist factions for the game.
If the player allies themselves with Silhouette however, he will work alongside them in Paris, France against the Majestic-12 Military Forces and presence in the country. JC Denton will encounter MJ12 troopers and will fight them alongside Silhouette however, since the leader of the organization is a member of the Illuminati, JC will be assisting the Illuminati in regaining its power if the player does the rigt decisions. Since Dumier moves on to become the Chairmen of the World Trade Organization in 2072, the organization either disbanded or got a new leader.