The study of the dynamics taking place during power system blackouts is a subject that receives contin-uous attention in view of its inherent complexity and relevant consequences. Within this context, thepaper aims at studying the role of the frequency control reserves (FCRs) on the cascading outages andthe relevant short-term dynamics associated with the blackout mechanisms. The relationship betweenthe large and small blackout frequency with respect to the value of FCRs is assessed. More in particular,the main contribution of this paper is to study the influence of the power system interconnections on itspre- and post-blackout behavior. For this investigation, a statistical procedure, based on the Monte Carlosimulation (MCS), is proposed. It performs a blackout risk analysis considering cascading outages as wellas generators/loads response to the frequency deviation. The proposed procedure is then applied to theIEEE 118 bus system as an interconnected network characterized by three areas. The distributions andexpected values of the blackout size are assessed for the whole system as well as for each area.