When you Invade, you aggressively take over or occupy a place. If a country's leader wants to gain more land, the military might invade a neighboring country.
Not everything that invades is militaristic. Some things that invade are cultural, such as the phenomena of young, stylish people moving into a neighborhood that had never been thought of as cool before. In an instant, new restaurants and shops catering to the newcomers open and soon the area is overrun with people wearing, say, skinny jeans and complicated eyewear. Natives to the area lament, "This place has been invaded by hipsters."