This paper proposes a methodology to split the power system across the weak areas of the network affected by a large disturbance, which might lead to a total system blackout. The final splitting strategy is carried out by opening the transmission lines with minimum power exchanged, i.e. by minimising the power exchange between areas. Since one or more of the created islands might reach an unstable operating point, and therefore, cause a power system blackout, the proposed methodology includes at least one blackstart unit within each island and assures sufficient generation capability to match the load consumption within each island. By assuring blackstart availability and sufficient generation capability, parallel power system restoration is planned in case of any eventuality. For validation purposes, the methodology is implemented and tested on the IEEE 9-bus and 118-bus test systems.