As time went on the area of trade widened until it covered whole countries, and finally expanded into international trade or commerce between different countries. [Sidenote: Inventions which have helped commerce to grow.] This widening kept step with improvements in the methods of transportation from pack-horse to wagon, from wagon to railroad, and from sailing vessel to steamship. The expansion of trade was also aided by the growth of strong governments which protected the trader and made the paths of commerce safe. Likewise the general use of money facilitated the operations of trade; so did the creation of a system of commercial credit. Without railroads and steamships, law and order, money and credit, it would not be possible to carry on commerce as we have it today. If the world can feed and clothe and shelter an enormously greater population than it could two hundred years ago this is not because the people work harder; it is because they work more intelligently and because they have created that gigantic system of economic co-operation which we call commerce. [Sidenote: Commerce includes exchange.] =The Scope of Commerce.=—It is an error to suppose that commerce is concerned only with the transportation of goods. Its scope is far wider. Commerce includes not only the moving of goods but the whole process of buying and selling. Wholesalers, jobbers, retailers, together with all those who work for them are engaged in commerce. Not only are the steamship lines, the railroads, and the motor trucks entitled to be called agencies of commerce, but the telegraph and telephone systems as well. The pipe lines which carry oil from the depths of the earth to the great cities are instrumentalities of commerce; so are the gas mains in the streets, the subways, and the street cars. The postal service, likewise, is one of the most important factors in expediting commercial transactions. [Sidenote: It depends upon currency and credit.] Commerce cannot be carried on, at least in any large measure, without currency and credit. Hence the whole system of money and banking links itself up closely with commercial organization. Goods are bought on credit by the wholesaler, and sold on credit to the retail merchant who, in turn, often sells on credit to his customers. The banks and other credit institutions provide the money to carry on these operations of trade. So when one takes all these things into account it will be seen that a considerable proportion of the people are engaged in one or another of the various branches of commerce. [Sidenote: Local, interstate, and international commerce.]