Complex sentence: According to the plans of the Main Command of the Soviet Military ("Stavka"), the two Soviet fronts would cut off vital Axis defensive lines in Northern Romania, facilitating a subsequent advance by the Red Army into the entire Balkan region.
Split into simpler sentences: According to the plans of the Main Command of the Soviet Military ("Stavka"), the two Soviet fronts would cut-off Axis vital defensive lines in Northern Romania. This then would facilitate a subsequent advance by the Red Army into the entire Balkan region.