Well, to me, as long as you're acknowledging that the Kwanggaeto stele is most likely referring to actions on the Korean Peninsula, and not among Korean colonies in Japan, I'm not really going to get up in arms.
However, regarding the strength of the Japanese, I would slightly dispute the matter. If according to the stele, Paekche isn't concluding a peace with Japan until 399, then who would the Wa have been allied with on the peninsula prior? Just Kaya? I find it hard to believe that Japan is occupying Silla cities after just a year after allying with Paekche. It just doesn't seem to me like that's reasonable. The 404 incursion mentions only the Wa; the parts where they're allied with Paekche's soldier is an addition by scholars based on the fact that it makes the most sense. But technically, not part of the stele we now have. As for Wa threatening the peninsula only in cooperation with other states, it doesn't seem likely to me if Wa is crossing the sea and threatening Paekche as it must have been doing before hand.
Well, no. You should probably read the entire text of the translated version when you have time. Baekje did conduct a treaty with the Wa in 399, but this treaty was
in violation of the mutual agreement in 396 between Goguryeo and Baekje, in which the latter agreed to cease hostilities, in exchange for Gwanggaeto leaving Wirye Fortress, the capital, alone. The stele itself says
nothing about previous agreements, of which archeological evidence, such as the seven-branched sword, says otherwise. The entire text itself is only recording bits and pieces of the entire story, of which it specifically states that Baekje and Silla were Goguryeo vassals that had continuously paid tribute.
However, this was far from the case, as the Samguk Sagi records that Baekje and Goguryeo had been continuously been in conflict from 369-396, during which in 371, Gogukwon became the only Goguryeo ruler to be slain in battle, and Gwanggaeto finally brought Baekje to its knees in 396 after surrounding Wirye Fortress. It's also curious that although the Samguk Sagi records Gwanggaeto's yearly clashes with Baekje from 391-4/5, the stele lumps them all together and records the results as if about 60 fortresses were captured in 396, which is logistically impossible.
In other words, although the record itself is reliable in terms of Goguryeo's viewpoints at the time, it is biased toward Goguryeo's exploits, which means that its losses were often minimized or omitted. It is certainly true that Gwanggaeto scored numerous victories against his opponents, but it seems to magically expand them back anachronistically, which seems unreasonable. The stele also omits any mention of the conflict with the Later Yan, which seems strange considering that Goguryeo confronted them several times, then eventually invaded the capital and occupied it for a short period of time.
In terms of the invasions in 400/4, the stele records that the Wa was chased back to Alla in 400, one of the cities of Gaya, which later surrendered, suggesting that some Gaya people were labeled as "Wa," or that there was an alliance between the two, as the Samguk Sagi does not state the Wa invading from Gaya or Baekje. Regarding the 404 invasion, it records "Baekjan" allying with the Wa, and scholars have agreed that the former was a derogatory word for Baekje, as "jan" has connotations of violence, and there was certainly no state named "Baekjan" at the time. Also, the term was also continuously used to refer to Baekje, while its actual name does not appear once in the text.
Well, this isn't convincing. The Tang navy isn't mentioned after the battle of Bisa, so it must have been attacked and destroyed by Koguryo's navy? Not a necessary conclusion to draw.
There are other issues, which I will not discuss in detail here, but the most notable one is that although Goguryeo casualties are recorded, Tang casualties
do not appear anywhere in the Book of Old/New Tang. Even if they were unrecorded due to the nature of the campaign, which is highly unlikely considering that those of Goguryeo were mentioned, one would expect later compilers to estimate the losses, but they are
nonexistent. Taizong of Tang is also recorded to have looked in the records of the expedition and edited them in order to make him look more favorable, which was unprecedented in Chinese history, as it introduced the ruler's biases. Of course, I'm not arguing whether the specific battles took place or not, but considering some of the omissions, some of the events were probably skewed, and other disasters were probably omitted altogether.
I'm also not convinced about Shin Chaeho's argument. I don't know where Simyang is, and I certainly can't think of sources he could have uncovered that nobody else found already, unless he's come across the equivalent of Korea's Bamboo Annals.
The sources, specifically Seogwak Japrok and Daedong Unhae, probably did exist when he compiled the records, but they are
no longer extant, like the ones cited in the Samguk Yusa, such as Baekje's Seogi compiled by Go Heung in 375, that we no longer have copies of. In terms of the latter, although the text cited numerous sources that are no longer extant, no one is questioning whether they were fabricated or not.
In terms of whether texts which have ambiguous sources are reliable or not, I'll provide a different example. Although I fully recognize that numerous passages of the Hwandan Gogi were either fabricated or copied verbatim from previous texts without making the necessary corrections, there are some points which other evidence has proved to be correct. The undisputed publication of the text occurred in 1979, but it states that Mun, a ruler of Balhae, had Daeheung as the era name. It was not until the following year that the tombstone of Princess Jeonghyo was discovered in Manchuria and stated the same thing, so considering that the records were compiled for some time before 1979, it must have relied on previous sources that are no longer extant. Another case is Jangsu's era name, Geonheung, which was previously stated in a Buddhist statue, but originally assumed to be that of a Baekje ruler before the Hwandan Gogi was published. The last is the mention of "five stars arranged in a straight line" in 1733 BC, and research proves that the incident occurred in 173
4 BC, which is only a year off.
Again, I acknowledge that the Hwandan Gogi makes numerous ridiculous claims, such as Gojoseon's population and size around 2000 BC, which are too large to be considered reasonable, along with stating that the state had invented an alphabet before the Chinese introduced its writing system. However, as the above evidence shows, some passages were certainly true, although it is unknown exactly which are fabricated/hold anachronistic viewpoints, and which are not, so the text
as a whole is unreliable.
By the way, I'm not arguing anything new. I still don't see any proof of how a Koguryo navy could help Japan. And it's not that I don't believe you, and it's not that I distrust you. But if I took everybody's statements on the forum at face value, I couldn't contribute to any discussion.
Well, it's much easier for you to state your points, because you're taking all of the historical records at face value, while I'm trying to convincingly reiterate some historians' viewpoints that there are notable omissions and biases which must be taken into consideration, which is much harder to do.