Are you implying that several hundred of people (guided by Hernán Cortés) killed 5 million of people?
The New Spain conquest (current Mexico) was done with the help of natives that hated Aztecs. Even with the help of gunpowder it would have been almost impossible to achieve that body count. Thus, the Spanish Crown wanted the help of the Catholic Church, so it promises keep the population to christianize them.
Not a lawyer but if you have signed a contract that clearly binds any development you do in your work laptop to your company you work for.
It is not a breach of contract but you have given intelectual property of any software you coded in your laptop.
I suppose you can speak with your manager and the legal team and ask them to release the code you coded with a license compatible with the project you collaborated. If the focus of that project is different from the focus/market of the company you can talk them into this and make them accept a once-in-a-lifetime exception.
There are some startups in Madrid[1], also, apply with LinkedIn and Glassdoor[2] to companies in Spain[3]. Speaking English and somewhat-entendible Spanish you shouldn't have any problem getting and interview. Indeed your English native level can be an asset.
Thus, you should bring to the interviews that have experience working in USA. I think that is pretty valued in Spain.
On the other hand, Madrid seems to have an American expat community, there are some meetups [4][5] and facebook groups, etc.
Differences between "Castillian Spanish" (I don't like that term at all, more on that on [1]) and Latin-American Spanish are only on pronunciation of some consonants. The Royal Spanish Academy (Real Academia Española) accepts allow all of those dialects as rightful variants of Spanish language.
[1] What some politicians call "Castillian Spanish" is the Spanish language spoken in all parts of Spain. It is idiotic to call "Castillian" to a language were some dialects of Spanish (West/East-Andalusian and Canarian [from Canary Islands]) are very similar to Latin-American Spanish.
Please, could you also educate them and tell them that Spain is a country in Europe? It seems that many US-americans believe Spanish is a race (whatever they think a "race" is) instead a nationality.
The contribution of Arabs to Spanish culture is enormous but that doesn't hide that in medieval times, almost everybody (including them) had barbaric customs.
[1] http://www.taipeitimes.com/News/world/archives/2004/07/18/20...
[2] https://inglesiesollosgrandes.blogspot.com/2012/05/emilio-ca...