Microeconomics and macroeconomics are closely intertwined. Because changes in the overall economy arise from the decisions of millions of individuals… - Greg Mankiw

The circular-flow diagram offers a simple way of organizing the economic transactions that occur between households and firms in the economy. The two loops of the circular-flow diagram are distinct but related. The inner loop represents the flows of inputs and outputs. The households sell the use of their labor, land, and capital to the firms in the markets for the factors of production. The firms then use these factors to produce goods and services, which in turn are sold to households in the markets for goods...

A few years ago, I had the good fortune of running across a first edition of Paul's textbook (not the recent reprint of the original text, but an actual 1948 edition). It was a real find. I bought the volume in an online auction for, if my recollection is correct, $35. Talk about consumer surplus! I would have gladly paid many times that.
At the next Boston Fed meeting, I took the book along to get Paul to sign it. Below is the book's title page, along with Paul's gracious inscription.

Countries as well as families benefit from the ability to trade with one another. Trade allows countries to specialize in what they do best and to enjoy a greater variety of goods and services. The Japanese, as well as the French and the Egyptians and the Brazilians, are as much our partners in the world economy as they are our competitors.