Equations describing plasma equilibria are derived from the total energy of the system. The MHD equilibrium is shown to hold even for systems where the magnetic field may locally vanish. Through conservation of helicity, confinement is shown to be intimately related to electromagnetic tension. For an axisymmetric device, the presence of a magnetic field or current circling the axis is shown to be destabilising. This provides a simple explanation for the poor performance of some devices for which MHD predicts stability.