The silk road could no longer be used because

After the great geographical discoveries in the late 15th – early 16th centuries the intercontinental overland trade routes fell into decay. The speed of the sea transportation, the possibility to carry more goods, relative cheapness of transportation resulted in the decline of the Silk Road in the end of the 15th century. Although some of its routes, especially those in the high-mountainous areas, connecting Tajikistan, Afghanistan, China, Pakistan and India, existed until the beginning of the 20th century. 

During the civil war in China the destroyed Silk Road once again played a big role.

River arrow on this map is pointing