The rhetorical device that is most clearly used here is "Ethos".
Ethos is known as a rhetoric device which is seen to appeal to ethics and to the credibility of the speaker. The speaker here makes his argument against the opposition of man and not making his own point of view. It's clear that the speaker uses 'ad hominem argument'. In this type of argument, the speaker tends to reproach the personality of the opponent.
As the speaker here uses "ad hominem argument", he tends to make himself to appeal credible to the audience. He makes his argument by criticizing his opponent, the Britain King. He argues that despite they have written petitions for a redress, their petitions were only answered by injury from Britain.
