Sentence:  That is the reason why I have asked you to take out and spread before you a map of the whole earth, and to follow with me the references which I shall make to the world-encircling <WSD>battle lines</WSD> of this war. 
Meaning of the word marked with <WSD> tags:  The notional line on either side of which opposing forces are arrayed, and at which they meet in battle; a fortified line, short of the line where battle is expected, and behind which forces are arrayed; a forward line of infantry or other force, prepared for battle.