some people are defending this because "anything goes" and "why couldn't there be a Korean bl series about American history", and I don't even really disagree with that. any kind of story can be told by and about anyone. but that doesn't mean or that it won't promote or reinforce lies, harmful ideas or that it'll be free from criticism.
anything's possible, so maybe this creator will turn out to have done their research and not be insensitive or ignorant, but I'm already skeptical due to the choice of character backgrounds. like of all the kinds of people and stories you could tell about this time period in this place, why are these the ones chosen? what's the appeal of their dynamic? why choose this setting and time period for that? if the creator hasn't done their due diligence, those questions will have very unflattering answers.
as it stands, it looks like a very deliberate choice to write around the existence of Black people who lived during that time even though their presence is integral to the livelihoods of the MCs. maybe the author thought they'd avoid the backlash they're now getting by doing that, but that's still an expression of racism, by ignoring that Black people are also people who want their stories and experiences told and treated with respect. and if the author didn't want to include Black people, which they're ultimately not obligated to do, they would have been better off choosing another topic and setting to write about, because like it or not, when writing about American history, you'll have to grapple with the racial dynamics of this country one way or another, to say nothing of the civil war era (even postwar) where the crux of the conflict was "what are we going to do with Black people (are they even people?)". to then make the only Black people in the story be faceless mobs seemingly only with the intention of making the white MC look good and ethical, just rubs salt in that wound. if the author wanted an interracial cowboy romance with this particular dynamic, they had other options for time and setting (and not to mention that those power and racial dynamics are present in other times as well).
every choice a creator makes in their story reflects their knowledge and interests, which are not free from bias. intentional or not, I see a lot of opportunity for missteps here.
I liked these threads for more background info - https://x.com/SPLover1863/status/2069382347972063697
https://x.com/SPLover1863/status/2069512321475465603
racism isn't always direct insults and targeted violence. it's also erasure and exclusion, putting particular people in particular roles. similar to how bullying isn't always physical violence, racism can operate in all kinds of subtle ways that can be hard to explain to other people if they aren't the target of it. many explanations have also been given in these comments for why people are reacting negatively to this.
while it's true that people shouldn't be looking towards fictional works for their primary history education, historical fiction is often a gateway to knowledge for many, and can shine a light on events, people, and topics in an engaging way that people might not otherwise get. I don't think lies and inaccuracies should go unchecked or without criticism, particularly when it comes this things like this that often unconsciously shape people's views and ideas of historical events and race, especially when they don't have much formal education on it.
what's the problem with people having conversations and talking about this.
presumably this doesn't matter to you, because you don't care, which makes me wonder why you're spending time on this.

Bro, I’m held back a lot LOL.. why does everyone hate this manwha? I thought everybody was ready for it.