Complex sentence: The merged city of Montreal was divided into 27 boroughs (known in French as "arrondissements") in charge of local administration, while the city above them was responsible for larger matters such as economic development or transportation issues.
Split into simpler sentences: The merged city of Montreal was divided into 27 boroughs (known in French as "arrondissements") in charge of local administration. The city government was responsible for larger matters such as economic development or transportation issues.