[Warning: Plot spoiler.]
Weber and Evans continue their Multiverse series with this second book. Much improved over the first, if only because it now has three things lacking in the former. A map of the network of Earths. A glossary of two sets of terms. (There are two different worlds that are clashing, and each has its own references.) Plus a list of characters. Of necessity, I still had to continually refer to all three while reading. But much more convenient than trying to keep a scad of unfamiliar names and relationships in my head. Which was the big drawback of book 1. Still, there is room for improvement in book 2. The main battle scene could have done with a map. Complicated enough to warrant this. Perhaps the authors don't think so. But they undoubtedly were conversant enough not to need it. It's different for the reader.
The plot of this book seems to be a reworking of the Pacific War, from Pearl Harbour to Midway. Arcana as Imperial Japan and Sharona as the US and its allies. To be sure, the analogy is not as close as in Turtledove's Civil War series, where the latest books are an explicit recap of World War 2. But the resemblences here are still striking. Arcanan diplomats stall negotiations long enough for their forces to launch a surprise attack. Much like Japanese diplomats in DC while their fleet approached Pearl. Arcana has air power, while Sharona completely lacks any such capability. Ok, here is one instance where the analogy does break down. The US, of course, had an air force. So you should not take the analogy too far.
More correlations arise. All the conflicts in this book take part on land. Initially, seemingly different from the Pacific, which were mostly naval conflicts. Actually, the book's battles are really akin to being fought over small islands vastly separated from each other. The worlds being explored are sparsely populated with Sharona and Arcana forts.
Another overlap is where Sharona's technology is roughly that of the US, between the World Wars. With the exception of electronics, where this has been replaced by psionics. So Sharona has the equivalent of radio and radar. Also, despite differences between Arcana and Sharona, the latter has far more logistical capability. Not a significant factor in this book. But it may come into play later. There is a strong hint of this in one character's observation. And I give nothing away by saying that there will be future books.
The overwhelming of the Sharona fort at Hell's Gate is the first battle of the book. How this occurred maps onto the attack on Pearl. One difference is that Arcana captures the fort, while Pearl never fell to the Japanese. (Though Turtledove has provided a history where this happened, if you're interested.)
Arcana then goes on to take a series of Sharona forts, mostly by surprise, with trivial casualties. These are the Japanese successes in the Pacific (Guam, Wake, Phillippines, etc) until Midway. Another correlation is in how the sides treat prisoners. Sharona does so humanely. But Arcana has several officers who deliberately torture and kill prisoners. Notably, not all the Arcana officers approve of this. But it is condoned as military necessity.
Finally, Midway. Sharona has a prince present at a key fort, with many soldiers and weapons. His visions of an Arcana attack are timely enough for his side to prepare and defeat it. The visions are the American breaking of the Japanese cryptography that told Spruance and Nimitz of the fleets approaching Midway.
Keep in mind that the analogy is thus far only in book 2. Book 1, while it laid the groundwork for this book, really did not use the analogy. And there is no guarantee or necessity for the authors to pursue this device in later books.
One possibly disappointing aspect to some readers is the death of the prince in the last battle. Used as propaganda by the Sharonan government to motivate its people. If you have read Weber's recent "On Armageddon Reef", he does a very similar action at the end of that book. While both scenes are well written, you can really see Weber at a figurative photocopying machine, simply pushing a button.