Qué significa 'habituamiento carnal'?
The context is the Spaniards colonizing México. This is part of the sentence in which I found it:
No podían crear habituamiento carnal con esclavas mayas al no estar evangelizadas.
4 Answers
Of course, they couldn't have sexual relations with Mayan slaves who had not been converted, so they baptised everyone in order to be able to have sexual relations.
Just in case:
while you are there, lookup "carnal" also.
Will this be "carnal knowledge"
all this has to do with cohabitation.
Claro, ellos no podían crear habituamiento carnal con esclavas mayas al no estar evangelizadas, así que deciden bautizarlas a todas, para poder hacer el habituamiento carnal.

I'll take a shot at the general meaning, although habituamiento is not in this dictionary, at least, and the construction "al no estar evangelizada" is hard to translate.
So,
They couldn't create carnal relations with mayan slaves upon not being envangelists,
which I infer to mean,
They couldn't create carnal relations with mayan slaves even though they weren't trying to convert them (to Catholocism).
Maybe a larger context is needed for a non-fluent spanish student to get this.
Lorenzo9 seems to have gotten the correct meaning. If you take evangelizadas to mean "converted", it makes complete sense. Literally:
No podían crear habituamiento carnal con esclavas mayas al no estar evangelizadas.
They couldn't have carnal relations with Mayan slaves who were not converted.