AFAIK Castro had never more than 3 thousand armed men at his side, and often much fewer, down to lower hundreds, spending much of the protracted conflict hiding in the countryside.

A revolution is something in which a significant part of a nation actively participates, not something that almost the entire population sits out passively.

Of course we can debate what is the necessary fraction, but 3000 militants isn't a big deal in a country of several million. Every Iraqi cleric in 2010 was able to put together a bigger militia than that.