This sentence is from the Woodrow Wilson's War Message to Congress (Joint Address to Congress Leading to a Declaration of War Against Germany (1917)).
The most likely purpose of including this in the last paragraph is to promote a sense of patriotism and to recieve a support from Congress for the war.
Wilson defended the American right to bring democracy and freedom to the world and that they must fight for "the liberties of the small nations". He also stated that the USA's neutral position was violated when the Germans announced submarine warfare against USA and United Kingdom.