Summer, 1996 -- The Ministry of Magic in London officially announce the return of Voldemort.
Spring, 1997 -- Quidditch matches are canceled indefinitely because of the constant threat of Death Eater attacks.
Summer, 1997 -- Voldemort attempts an attack on Hogwarts to kill Albus Dumbledore and fails. Remembering the prophecy that before he can really continue, he must first kill Harry Potter, Voldemort orders Potter found and brought to him. Harry, though safe with his aunt and uncle, is sent to Hogwarts in August for added protection.
Spring, 1998 -- Harry is finally captured after the betrayal of several students and brought before Voldemort. Harry is killed before he can even draw his wand, and Voldemort is free to continue his slow take over of the world.
Autumn, 1998 -- Voldemort takes the Ministry of Magic in London, and those loyal to the side of good, which as it turns out are few in number, scatter into the countryside, depending on owl post to get any work done at all. Eventually, they congregate at Hogwarts, then Glasgow, setting up permanent residence there.
Winter, 1998 -- Voldemort's forced capture almost all of Wales, and any pockets of resistence are stamped out before they can truly organize and fight back.
Early winter, 1999 -- Voldemort begins the North March, intent on taking Hogwarts.
Spring, 1999 -- The Battle at the Wall is fought to a standstill, and Hadrian's Wall is used as a bored between light and dark.
Summer, 1999 -- sporadic assaults on the Wall result in nothing gained on either side. The war is completely at a standstill. The Daily Prophet compares it to the muggle World War I with the trenches, with no ground lost and no ground gained.
Autumn 1999 -- Lucius Malfoy sends a notice to Dumbledore wishing to talk peace. They meet in Dublin, and, obviously, it was a trap. Dumbledore knew this, but went anyway, and was killed.
Winter 1999 to Present Day, 2003 -- scattered opened and guerrilla warfare. However, despite the efforts of spies on both sides, no ground has been gained since 1999, and Hadrian's wall still stands as the border between them.