The dynamics of power system blackouts and the associated Self-Organized Criticality (SOC) behavior is a subject that receives continuous attention in view of its inherent complexity and relevant consequences. Within this context, the paper focuses on the short-term dynamic and, more specifically, aims at studying the role of the spinning reserve and frequency control on the blackout mechanism. The main contribution is to study the influence of the power system interconnections on the pre and post blackout system behavior. For this investigation, a statistical procedure, based on the Monte Carlo Simulation (MCS) method, is proposed to perform a blackout risk analysis considering cascading outages and generators frequency responses. The proposed procedure is then applied to the IEEE 118 bus system as an interconnected network characterized by three areas. The distribution of the blackout size and the number of component outages are assessed for the whole system as well as for each area.