Introduction. The comparison method in the qualitative theory of equations is of paramount importance in studies of large-scale systems. This method is based on differential inequalities such as the Chaplygin-Wazewski inequality and Lyapunov functions (scalar, vector, or matrix-valued), which play the role of nonlinear transformation of the original system to an equation (a system or a matrix system) of lower dimension. The comparison method states that if for the system in question, there exists a Lyapunov function (scalar, vector, or matrix-valued) satisfying appropriate conditions, then various dynamic properties of the solutions of the original system follow from the respective dynamic properties of the comparison system.Thus, the stability analysis of a dynamic system involves setting up a Lyapunov function and establishing stability criteria for the zero solution of the comparison system.The present review discusses some approaches to solving such problems, establishes a uniform asymptotic stability criterion for a nonlinear comparison system, and exemplifies its applications in modern nonlinear dynamics.1. Problem Formulation. Let x t ( )be an n-dimensional state vector of some mechanical system with a finite number of degrees of freedom. Its behavior is described by the perturbed equations of motionwhere a, b are positive constants and j( ) t is a bounded nonnegative function. This equation cannot be integrated analytically, but using it leads to a number of interesting results for both system (8) and uncertain systems (see [30] and the references therein).3. System of Comparison with Vector Lyapunov Function. The curse of dimensionality in the sense of Bellman (see [8]) in the qualitative theory of equations makes it impossible to set up a scalar Lyapunov function for a large-scale system. In these conditions, Kron developed diakoptics [22] for the analysis of complex systems by parts. This method is based on the concept of a vector Lyapunov function and corresponding comparison system.Recall the following concept from the theory of monotonic systems (see [98]).