Looking at modern French in light of vulgar Latin, or Chinese compared with Proto-Sino-Tibetan (if that can even be reconstructed), there seems to be quite a few contexts in which phonemes are subsumed, vowels are nasalized to indicate the loss of a nasal, or tones are introduced to retain distinctions formerly maintained by distinct consonant clusters. Modern Celtic languages certainly seem to have done a lot of this too, and I have heard that a similar thing happened in Sumerian.
I was wondering if anyone has any theories or reference to theories about
(1) What makes a language "prepared" for such a phenomenon to occur (e.g., are there some languages that this would be much less likely to happen to?)
(2) Whether there are any aspects of a culture speaking a language that make people more likely to gravitate towards doing something like this across whatever number of generations.
(I would also be interested in hearing whether anyone believes there was the strong presence of a Celtic substratum in French that influenced it in this way, but that's kind of tangential.)