It's pretty simple---God made a few language families at Babel then dispersed them worldwide. Based on a few factors it wouldn't be long for Languages within the Language families to begin the diversification process within each family.
1- And hath made of one blood all nations of men for to dwell on all the face of the earth, and hath determined the times before appointed, and the bounds of their habitation;
Acts 17:26
2- Therefore is the name of it called Babel; because the LORD did there confound the language of all the earth: and from thence did the LORD scatter them abroad upon the face of all the earth.
Genesis 11:9
"Among the five factors, geographical isolation exerted the 
strongest effect on overall lexical differentiation, significantly increasing its pace (estimate = 1.09; 90% HPDI: [0.92, 1.24]).
This is because although it moderately increased the ability at which languages acquired new lexical items (estimate = 0.29, 90% HPDI: [0.06, 0.51]) it also severely increased the rate of word loss (estimate = 0.86, 90% HPDI: [0.70, 1.04]).
In the models, the languages of cultural groups with larger populations gained words at a faster rate (estimate = 0.52, 90% HPDI: [0.34, 0.68]). Although we also found evidence that these languages also lost words at a slightly faster pace (estimate = 0.14, 90% HPDI: [0.08, 0.20]), the overall positive effect of speaker population size on lexical turnover was not significant (0.06, 90% HPDI: [-0.10, 0.23]).
Conflict between communities of the same culture reduced words gains (estimate = -0.30; 90% HPDI: [-0.50, -0.11]) but increased the pace at which languages lost words (estimate = 0.37; 90% HPDI: [0.16, 0.58].
Although population size did not have an effect on the overall rate of linguistic differentiation, larger population sizes increased the rate at which languages acquired new vocabulary items. ... may also be due to large populations having less stringent norm enforcement allowing them to change fast.
We identified patterns of word gain and loss by recording instances where a cognate form within a given semantic category was present in one language of a sister pair but not in the other.
---If a word form found in one sister language has a cognate in other languages in the language family, it is likely to have been inherited from the common ancestor. This implies that the absence of that cognate form in the other sister language must be due to its loss after divergence from their exclusive common ancestor.
---On the other hand, if one of the sister languages has a unique word form with no recognized cognates in any other language in the family, it presumably represents a gain of a new word since the split from its sister language.
The difference in the number of word gains and losses between
languages in each pair was modeled as a Poisson distribution, where the expected number of differences in words gained or lost is a log-linear function of the main effects β. We adopted regularizing priors that are more conservative than the implied flat priors of non-Bayesian procedures, which prevents the model from overfitting data]."
Cecilia Padilla-Iglesias, /Erik Gjesfjeld, /Lucio Vinicius-PLOSonelanguages in each pair was modeled as a Poisson distribution, where the expected number of differences in words gained or lost is a log-linear function of the main effects β. We adopted regularizing priors that are more conservative than the implied flat priors of non-Bayesian procedures, which prevents the model from overfitting data]."