People actually did use routes similar to the Silk Road for long-distance trade well before 1400.

China was in fact actually connected to the Mediterranean via trade routes as you can read in this blog post from a site in Israel. Additional Chinese imports were recovered in 2012, from deposits in the Fatimid period, late 10th-11th century AD. You can read about that very briefly in the excavation reports here (PDF warning) on page 5. So the Islamic period civilizations had connections to China well before 1400.

But long distance trade was established far earlier than that. For example, one excellent example of a well-established long-distance trade route was between the Assyrians (in modern Iraq) and the Hittites (in modern Turkey) around 1800 BC, where traders would exchange goods from Assyria in exchange for silver in a specialized merchant colony in the city of Kanesh. You can read further about the trade network here.

Long distance trade can happen in different ways. You can have merchants directly traveling from one place to another and transferring goods (called direct trading) or you can have those goods make several stops as they filter their way down into more inaccessible areas, as a person who buys the goods from the trader then travels a little and sells them to another person, who does the same.

We know that ancient Near Eastern people working bronze had to import tin from somewhere, as there are very few (basically none) tin mines in the Near East. They had to import it from Afghanistan or a couple places in Turkey. Again, this is probably the result of some down-the-line trading in earlier times.

We have examples of artifacts traded down the line from the Indus Valley found in the Near East, as there were very plentiful carnelian deposits there (Arkell, A.J. (1936). "Cambay and the Bead Trade". Antiquity 10. 292-305).

Both of these methods were used in antiquity, and both were probably used on the Silk Road.

Therefore, very long-distance international cross-continental trade along established routes took place long before the Silk Road began.

By the way, the Silk Road began in around 200 BC, not 1400 AD.