The United States conquering all of Mexico - it would be possible to take the entire country, but not to hold in the long run.
The Confederacy gaining independence, and then shortly after abolishing slavery - This one's a twofer, since it's unlikely they'd get independence in the first place, and if they did it would be even less likely to turn around and end slavery. Yes, the civil war was about states rights, but more specifically it was mostly about states rights to own slaves.
Various nations "pulling a Meiji" - There were very specific conditions in place that allowed Japan to rapidly industrialize, and unfortunately not very many other nations had them. With the right POD, of course, it would be possible to put those conditions into place, but many people only seem to be interested in a POD in the 1800s, after it's too late for many areas.
It's probably not right to call all of the above outright ASB... but then I am very hesitant to call anything ASB short of divine or extraterrestrial intervention. It would just be a very uphill battle to properly explain and plausibly justify them in any TL.