At the beginning of the Pilot, humans are engaged in active battle with Skitters and Mechs. At one point, during a human partial retreat, one young woman runs full tilt at the fighters, yelling: "South Boston! South Boston! They've just taken South Boston!". South Boston contains Dorchester Heights, where George Washington forced British troops to evacuate during the American Revolutionary War. So this would indicate a serious conquest for the aliens - taking a section of human real estate with such distinct historical value.