I think it'd be a shame not to run this on (almost) current day Khorvaire. There are some alterations to geography and history that would be needed, but nothing major.
Now admittedly, I'm basing my decisions on mostly the first few advenutres and the Campaign Guide, so I may need to make alterations as I find out more.
First, Marguul Pass takes the place of Gate Pass and the Battle of Marguul Pass during the Last War did not occur as written in Forge of War. Formerly belonging to Cyre, Marguul Pass was annexed by Breland when Darguul declared it's independence. During the remaining 30 years of the Last War, the city passed between Darguul and Breland several times. Finally fed up with the war, Marguul Pass declared itself an independent city and despite a few meager attacks by the two neighbouring nations, managed to keep its independence. It's independence was codified in the Treaty of Thronehold.
Next, advance the timeline by about 10 years.
Breland is Ragesia.
Late in 1003 King Boranell died. Lord Ruken ir'Clarn succeeded in his plot to turn the monarchy into a ceremonial position and was voted as the country's first prime minister to be head of state. However it was not to last. On his first trip to Sharn after his election to celebrate the new democracy, he, his entire cabinet, Boranell's heirs and about 40,000 other victims died in the most horriffic terrorist attack in history.
An eldritch device of immense power nullfied the manifest zone of Syrania in the heart of Sharn. Without the influence of the plane, Skyway and the entire Central Plateau collapsed into ruin. Accusations and incriminations shot out among the Dragonmarked Houses and all the nations of Khorvaire.
The Last War may have restarted right there if it weren't for the fact that people still feared another Mourning. With no civilian government, General Coaltongue, one of the most decorated soldiers of the Last War (and in fact, he fought during the first battles over 100 years ago) took control and declared martial law. In shock, the population accepted this situation.
Breland has spent two years recovering from the disaster. There continued to be calls for revenge for the disaster but strangely, it was impossible to discover who or what was responsible for the attack. Becoming more and more paranoid, Coaltongue at the suggestion of his friend Leska, created the Inquisitors whose mission was to investigate enemies of the state.
Eventually in the ruins of the towers, the cause of the disaster was discovered. The eldritch device that destroyed the towers was discovered to have been powered by arcane energies. A pogrom was instituted in Breland, imprisoning arcane casters.
Finally, Breland was ready to start going to war with the goal of attaining the throne of Galifar, which many believed that Breland could have done earlier, if it merely had had the will.
At the recommendation of Leska, Coaltongue decided to make Droaam his first conquest, recovering part of the territory Breland had lost when Droaam declared independence. The Sisters of Sora Kell refused to surrender but strangely the monsters of Droaam did not put up much organized resistance. However, the Sisters were never captured and have disappeared Breland then absorbed Droaam back into the country and added the monstrous troops to its armies. In truth, Leska is actually Sora Katra, one of the sisters of Sora Kell. It actually was she and her sisters that orchestrated the disaster in Sharn, all in a long game attempt to take control of Breland themselves.
Shahalesti is Darguul.
In 998 Ruus Dhakan united the clans of the Dhakaani. The Dhakaani planned their conquest over the Ghaal'dar and struck in 999 when the Lhesh Haruuc died. With their superiority in combat and ancient artifiacts the Dhakaani quickly conquered the rest of Darguul. Over the past 10 years they have striven to develop a navy, improving the army and increasing their mastery of the arcane arts
Attempting to improve their diplomatic status, Darguul quickly sent aid to Breland after the great terrorist attack. This significantly improved the relations between the countries...until recently as Breland became more and more militant. Darguul has spent the last year preparing for a war that they expect to come soon.
Zilargo is Dassen.
Seaquen is actually the feyspire Pylas Pyrial, with some slight geographical modifications to create a peninsula with a swamp for it to be on.
Thrane is Sindaire.
Aundair is Ostalin.
