The Age of Ra, by James Lovegrove.
Renting this from the library, as I saw the two sequels in Waterstones (although, I don't think the books in this series have a shared world). The basic premise is that around Edwardian times (the book gives a rather vague "a little over a century ago"), the Egyptian Pantheon wiped out every single other figure of worship, leaving them the world's ONLY religion.
The world was split, with Osiris and Isis having Britain and Europe, Set having Russia and China (Red countries... hahaha), Anubis having Japan and "south east Asia", Horus having North America (his offspring got South America... it's implied to not be a nice place to live because of it), and Nephthys having Africa and "Arabia".
The only place not under the control of the gods is Egypt, renamed Freegypt, as there was a lot of controversy over who got their birthland. The other Egyptian gods also still exist (in differing degrees, based on the strength of their worship), but it's implied those are the only ones who control mortal lands (no, I don't know about Oceania). Those gods in charge of mortal lands are having their subjects fight based on their own conflicts and alliances.
The book has two viewpoints so far - Lt. David Westwynter, a British soldier on a covert insert into Nephthysian territory, which quickly goes south (literally), and Ra, the sun god, who is trying to bring peace to his feuding family.
Quite enjoyable, I'm planning to pick up both Age of Zeus and Age of Odin after this.