What is the theme in The Story of Mankind by Hendrik Willem Van Loon?

Military Expansion is another theme in the book. The theme of governmental expansion has dominated history for thousands of years, and is a primary theme within the novel as a result. As early as 39 B.C., the Hyksos attack Egypt to expand their empire, and the Romans continue until they capture Egypt in that year. The Persian wars are based on the desire of the Persians to control the Greeks, and to expand the Persian empire through lands owned by the Greeks. Alexander of Macedonia expands his empire to include Egypt, Phoenicia, Persia, and the Himalayas.