Rigorous Proof of a Liquid-Vapor Phase Transition in a Continuum   Particle System
  We consider particles in ${\Bbb R}^d, d \geq 2$, interacting via attractive pair and repulsive four-body potentials of the Kac type. Perturbing about mean field theory, valid when the interaction range becomes infinite, we prove rigorously the existence of a liquid-gas phase transition when the interaction range is finite but long compared to the interparticle spacing. 
J. L. Lebowitz, A. E. Mazel, E. Presutti