Complex sentence: Stambolov negotiated loans with Western European countries in order to develop the military strength of Bulgaria and create a modern army which could successfully unify the national with the support of the Bulgarian national uprising in Macedonia.
Split into simpler sentences: Stambolov negotiated loans with Western European countries in order to develop the military strength of Bulgaria. In part, this was motivatied by his desire to create a modern army which could successfully unify the nation with the support of the Bulgarian national uprising in Macedonia.