1.march aggressively into another's territory by military force for the purposes of conquest and occupation;
Hitler invaded Poland on September 1, 1939
2.to intrude upon, infringe, encroach on, violate;
This new colleague invades my territory
3.occupy in large numbers or live on a host;
the Kudzu plant infests much of the South and is spreading to the North
4.penetrate or assault, in a harmful or injurious way;
The cancer had invaded her lungs