How can you say that wholesale and retail trade are the part of internal trade?

Most of the producers are not in a position to sell their goods directly to the consumers a chain is required which acts as a connecting link between producer and consumers that directs the flow of goods from centres of production to centres of consumption. In this context, wholesalers purchase goods from the producers and sell them to retailers and retailers sell the goods to the consumers in this way wholesale trade and retail trade become the part of internal trade.