The US government 1776-1865 is obviously democratic, and it's obviously possible (and again, not uncommon) for a democracy to engage in disenfranchisement. Your objection is a form of the "No True Scotsman" fallacy in that you are attempting to define democracy as a non-authoritarian system which is demonstrably false.

In any event it's not necessary to argue this point because there are no shortage of further examples which include authoritarianism exerted over non-disenfranchised demographics. Here are some further examples of authoritarianism within the USA:

* Japanese internment of 1940s

* Every historic invocation of martial law (more than a dozen)

* Every historic invocation of conscription

* Historic oppression of women, which continued well after the suffrage movement in a variety of ways

There are of course countless other examples throughout the history of democracies. Even a cursory reading can uncover countless examples, from contemporary democracies all the way back to its origins in ancient Greece. It is not uncommon for a majority rule system to impose authoritarian controls -- in fact, it is the norm. This is why we have concepts such as constitutional rights, which are specifically designed to balance against the authoritarian tendencies of majority rule.