Answer:
The system of trade that was most widely used in both ancient river civilizations and ancient Native American civilizations was bartering.
Bartering is the exchange of goods or services without the use of money. In ancient river civilizations such as Mesopotamia, India, and China, bartering was used to trade goods such as grain, pottery, and textiles. In ancient Native American civilizations, bartering was used to trade goods such as furs, food, and tools.
While some ancient river civilizations did use coined money, it was not as widespread as bartering. Free exchange and international trade were not common in ancient times due to the lack of transportation and communication technology.