Why did the north vietnamese send soldiers to south vietnam?

Supplies were carried almost entirely by human porters, with some use also being made of bicycles, elephants, and pack horses. When a Transportation Group first worked on the trail during the summer of 1959, the Trail passed south through the western portion of the Special Zone, crossed the between North and South Vietnam at the Ben Hai River and continued through the rugged mountains of western provinces in South Vietnam. 

The correct answer is kettles.

B  maybe the answer hoped it