Sentence:  After a White House huddle between the President and top lieutenants , the Defense Department reacted sharply to a cry from the pro-Western government of Laos that several battalions of Communist troops had <WSD>invaded</WSD> Laos from North Viet Nam . 
Meaning of the word marked with <WSD> tags:  march aggressively into another's territory by military force for the purposes of conquest and occupation