It totally excuses it. Intent is key. If you have no clue what a disease, a virus, an immune system are I don't see how you can be called "heinous" for unknowingly and unwillingly spread diseases.

As for lands, I don't know, lands all over the world have been changing hands since human beings learnt how to walk, most of the time after violence/war. It happened in 1500 when the concept of "nation" didn't even exist and the only way to say that a land was yours was to be able to keep it.

Well, then China is responsible for mass genocide due to Covid-19 then. After all, whether or not they knew they were transporting disease to other countries 6 months back really doesn't excuse the end result.

But that happened in the 18th century though, by then of course, empirical observation had played its role and a few people tried to weaponize it. I'm pretty sure accidental contamination during the 2 preceding centuries had already caused a massive decline in population.