Final answer:
The Grand Canal was an essential transportation route for the Chinese empire under the Sui dynasty, providing economic integration, improved communication, and a tool for foreign policy.
Step-by-step explanation:
The Grand Canal was essential to the economic and administrative integration of the newly reunified Chinese empire under the Sui. The canal made it easier for goods to be transported and provided increased revenue by allowing the government to tax the products being shipped. It also greatly improved communication and the effectiveness of the government, as officials were able to travel quickly between north and south and to send communication more easily across the Chinese interior. The canal was also a vital tool of Sui foreign policy, allowing Chinese armies from the north to travel to the borders of Korea, from which Yang Di launched his futile campaigns of conquest.