I. England and Wales fell under the Dark Lord's control in the year 1999, a year and a day following the death of Harry Potter. However, through the efforts of a band of wizards loyal to Dumbledore, the Dark Lord's advance north was stopped at Hadrian's wall, the old Roman wall that marked the end of the northern edge of the Roman Empire.
Death Eaters constantly attempt to invade past the wall, basing their largest grouping of men in camps near the Wall. However, they can't get past the wards in large groups, and have to settle for one man spying missions.
The capital of this faction lies in London.
II. Scotland and Northern Ireland are in the hands of the band of wizard's known unofficially as Dumbledore's army after the late Albus Dumbledore. The lands spread north from the Roman ruins of Hadrian's Wall, and the section of the Irish Sea which lies between the two islands is closely guarded to prevent a marine attack from the south.
The border between Northern Ireland and Ireland is kept safe due to highly powerful ward, much like the antiapparation wards the used to lie around Hogwarts. These same wards cover Hadrian's Wall between England and Scotland.
The capital of this faction lies at Glasgow.
III. Ireland is neutral, but not really. It's more of a No Man's Land. Any wizard found roaming in this country is subject to immediate suspicion no matter what, and will most like be hunted and killed by a group that calls itself Captain Moonlight, after the Irish Independence militant group of the 1800s.
Dublin, however, is true neutral ground and is the new location of St. Mungo's Hospital for Magical Maladies and Injuries. It is also the location for any and all negotiations in this war.
IV. The Continent is truly neutral in this war, mostly because the Magical governments are terrified of an all out war spreading through Europe again. However, Beauxbatons has agreed to take in the British wizarding students who otherwise would get no magical education.