I suppose that an alternative interpretation of the sixth trumpet would be to see it as announcing the French Revolution, and, more generally, the advent of secularisation.  On this account, the loosing of the angels at the Euphrates, that is, the elimination of the protective shield between the Church and the World, would be identified with the dissolution of Christendom.  The precise ‘day and hour’ when everything kicked off might be identified with the decision of King Louis XVI not to break up the self-appointed tennis-court assembly, or perhaps with his own execution. 

On the other hand, while the Revolutionary wars, and the wars of national self-aggrandizement which they spawned, killed a large number of people, it does not amount to ‘a third of mankind’, at any rate, not yet.  There is also the point that secularisation is a logical consequence of Protestantism, and in that sense M. Robespierre and his friends would seem to pertain rather to the fifth trumpet than to the sixth.  Gregory XVI implies this in Mirari vos:

This shameful font of indifferentism gives rise to that absurd and erroneous proposition which claims that liberty of conscience must be maintained for everyone. It spreads ruin in sacred and civil affairs, though some repeat over and over again with the greatest impudence that some advantage accrues to religion from it. “But the death of the soul is worse than freedom of error,” as Augustine was wont to say. When all restraints are removed by which men are kept on the narrow path of truth, their nature, which is already inclined to evil, propels them to ruin. Then truly “the bottomless pit” is open from which John saw smoke ascending which obscured the sun, and out of which locusts flew forth to devastate the earth.