What is happening on the East coast and in the centre?
The ROKs are manning the front everywhere east of Wonju (roughly half way between the east and west coasts), with the front somewhere between 37*20' (Wonju) and 37* (Ulchin) in the ROK sector. At this stage they are pushing north about as quickly as Patton's troops.
I am really not well versed in Korean War, so can somebody explain the differences between OTL and TTL so far? It looks like Allies have advanced faster then IOTL, and have managed to destroy/surround larger numbers of N.K troops?
@Darrenb209 summed it up pretty well (although I will note September 14 was the date where the UN held the least territory IOTL, so it does sound a little dramatic - the front ITTL Sept 15 is roughly where it was IOTL Sept 27 or thereabouts).
The biggest difference ITTL is that the battle of Taejon (covered in Ch4 and thereabouts) resulted in a UN retreat IOTL, whereas here Patton holds it. OTL Taejon allowed the NK army to secure a couple of key roads that it used to rush a series of locations on the west and then southern coasts, which eventually resulted in the western side of the Pusan perimeter being formed where it was - ITTL Patton had artillery ranged on those roads within a couple of days of them breaking out, more or less cutting them off from supply and forcing a division or so worth of troops to surrender. It also means his counterattack started from a much more forward position, about 36*30' instead of 35*50', and much further to the west as well.
Patton has also started his counterattack a full two weeks earlier than OTL Walker did, albeit against (slightly) stronger opposition than Walker faced - this is due to the NK not having been worn down quite so much by their own failed offensive ("The Great Naktong Offensive" if you want to look it up). Inchon has to be the date it is because of the tides, but IOTL the Pusan and Inchon forces were quite separated by this time - ITTL Patton had (just) captured the landing beaches.
"Under the hood" Patton has also made a lot of improvements to things like training, logistics, intelligence &c. IOTL all these things ranged from poor to extremely terrible (Walker had at least twice the manpower and many times the amounts of equipment as the North Koreans in September, yet he didn't attack in strength basically anywhere until after Inchon). ITTL, every time I mention one of these things in any sort of detail, it is a change from OTL (and usually they are things that Patton remarked upon in his book
War As I Knew It, which I strongly recommend reading if you are interested in his style of command!). The opposite goes for any diplomatic relations between the Eighth Army and Rhee - IOTL Walker never had any issues with Rhee (or vice versa) and the ROK military was at times very well integrated with the US Army (indeed the KATUSA program continues to this day!), and as far as I'm aware neither Truman, Attlee* or anyone else had a problem with Walker either (MacArthur didn't like the Bulldog much, which is why X Corps and 8th Army were kept as separate commands IOTL). All the diplomatic issues between Patton and just about everyone are TTL-specific.
* On the topic of Attlee, he didn't think very highly of MacArthur at all, while he didn't have much to do with Patton due to the latter's death early into his term. The Commonwealth brigade was integrated into 8th Army both TTL and OTL, but the "keep it separate from MacArthur" is a TTL addition only.
If you're interested in learning (a lot) more about the Korean War, I recommend
South to the Naktong, North to the Yalu by Roy E. Appleman, which you can read for free here:
https://history.army.mil/books/korea/20-2-1/toc.htm - it has been my go-to source for a lot of the events of the war (most of my other research has been biographies of Patton and MacArthur) and is both extremely detailed yet also easy to read.
- BNC