During the following summer, with Dumbledore dead, the ministry predictably fell, and Harry spent half a year leading lone guerilla warfare, taking a page from the Death Eater's book. It helped to sharpen his skills and magic further whilst also searching for the whereabouts of the Horcruxes. Slowly but methodically, he decimated Voldemort's followers. It was easy enough with all his current skills and tools in his possession. Ambushing unaware people was much easier than fighting them to the death directly, and evened his odds against multiple opponents.