It's a shared world (Fantasy) anthology series.
Magic can only be accessed by blood-letting. For centuries, the vorteciens commanded the known world, using people as sacrifices as they pleased. While the people fought back, they could not win. Not until one of the greatest vorteciens of all time turned against his own kind and created the tereges (plural of terex, which is what's in the picture), which allows normal people access to magic without sacrifice. A war ensued between the magic-using Cadre and the vorteciens. In time, the vorteciens were beaten back.
Several hundred years later, people believe that the vorteciens are gone forever. They grow nervous about having the Cadre around, because magic is corrupting and they don't want to be ruled by magic users again.
Most of the stories in the first issues focus on the Cadre d'Florant (it's a French-influenced word, think Louis XIV) and the conflicts between their duc and the Duc d'Lascelles after a Florantian terex claims a rather--ill-advised partner.