We present recent results concerning the entropy dynamics of black holes and democratic systems. Democratic systems are those maximally non-local many-body systems, in which every degree of freedom interacts with every other degree of freedom through couplings of the same size. They include large-N matrix models and the Sachdev-Ye-Kitaev model, both expected to be potentially realistic models of black holes. The results will be obtained within the simplest (still non-trivial) democratic system, a model of "random particles". The outshot is that large-N factorization is equivalent to extensivity of entanglement evolution, providing a specific formula for the entanglement dynamics of any subsystem, up to subleading corrections in the thermodynamic limit. These results extend to any democratic system since large-N factorization is a characteristic property of these models. We end up by presenting novel aspects of black hole entropy evolution, using the Bekenstein-Hawking formula, and compare the results of the two approaches.