Precise measurements of the static magnetic susceptibility have been made by the Faraday method over a range of temperature from 1.6 to 300 K on a series of niobium-substituted vanadium diselenides. The kink anomaly associated with onset of the charge density wave at 117 K in VSe2 is observed to move to higher temperatures as the niobium concentration is increased. In addition, plateaus appear in the susceptibility versus temperature curve below the onset temperature. It is suggested that the plateaus are due to stepwise destruction of the Fermi surface. A transition to the commensurate state is observed at about 75 K in pure VSe2; it is relatively insensitive to the doping level and is observed as an anomaly in the magnetic susceptibility even at a 10% doping level.