This paper investigates a two-dimensional mathematical model for the spreading and stability of a thin film of an incompressible Newtonian liquid on a rigid horizontal plane. Utilizing the lubrication approximation, the model is formulated through a nonlinear fourth-order thin-film equation that describes the primary physical forces acting on the film, namely capillary pressure, gravity, and intermolecular forces incorporated through an explicit disjoining-pressure term. The dimensionless equation reveals that the Bond number, which represents the relative role of gravity, is the only important remaining parameter. The results indicate that surface tension and gravity stabilize the film by suppressing disturbance growth, while attractive van der Waals forces can amplify long-wave disturbances and may lead to spinodal dewetting