The luxury liner as a means of transport would also succumb, in its turn, to the relentless march of technology. Both world wars contributed to the American taste for foreign travel by exposing millions of service personnel to the excitement of faraway places. International tourism as a giant industry did not get under way until the 1950s, however. Jet speeds not only made accessible places that were previously considered remote, such as the South Pacific, the Far East, South America, and Africa, but also opened up the world of international travel to ordinary working people, who normally had only two weeks' annual vacation time at their disposal. Tourism differs from travel as leisure differs from labor.
People travel for any number of reasons, from business to war or religion.
Tourism, however, is travel undertaken for pleasure. Depending on individual tastes, it may involve rest and relaxation, sports, cultural exchanges, educational and aesthetic experiences, or eating and shopping. As a modern multimillion-dollar business, it caters to the tourist's need for transportation, accommodation, food, entertainment, recreation, health, souvenirs, and social contact. Mass tourism is a relatively modern phenomenon, but travelers have reacted as tourists, regardless of the purpose of their journeys, since the beginning of recorded history. To write his history of the war between the Greeks and the Persians, Herodotus personally visited many of the areas making up the Persian Empire.