Sentence:  Though the number of people flowing in and out of our metropolitan areas each day has increased tremendously since <WSD>World</WSD> War 2 , , total annual rail commutation dropped 124 million from 1947 to 1957 . 
Meaning of the word marked with <WSD> tags:  a war between the Allies (Australia, Belgium, Bolivia, Brazil, Canada, China, Colombia, Costa Rica, Cuba, Czechoslovakia, Dominican Republic, El Salvador, Ethiopia, France, Greece, Guatemala, Haiti, Honduras, India, Iran, Iraq, Luxembourg, Mexico, Netherlands, New Zealand, Nicaragua, Norway, Panama, Philippines, Poland, South Africa, United Kingdom, United States, USSR, Yugoslavia) and the Axis (Albania, Bulgaria, Finland, Germany, Hungary, Italy, Japan, Rumania, Slovakia, Thailand) from 1939 to 1945