On this day in 1916, U.S. federal authorities arrested two German agents in Trenton, New Jersey on suspicion of sabotage.

Under question the agents were discovered to have been plotting to bomb the Black Tom Island munitions factory near Jersey City; this discovery further soured already acrimonious U.S.-German diplomatic relations and pushed the United States and Germany one step closer to the brink of war. America would finally step over the brink four months later with the disclosure of the infamous Zimmerman telegram.

On this day in 1915, engine troubles forced the British steamship Lusitania to cancel a scheduled transatlantic voyage to New York City. Inconvenient though it might have seemed at first glance, however, this incident turned out to save the lives of her passengers and crew; three days later another ship traveling on the same route Lusitania was to have taken to New York got torpedoed by a German U-boat.

On this day in 1915, British prime minister David Lloyd George received news from his top counterintelligence advisors that evidence had been uncovered suggesting the passenger ship Lusitania had been intentionally targeted for sinking by the Imperial German Navy.

On this day in 1915, the military attaché at the British embassy in Washington presented U.S. President Woodrow Wilson and Wilson's Secretary of War, Newton D. Baker, with evidence suggesting the Lusitania had been purposely singled out for submarine attack by the Imperial German Navy in attempt to intimidate the United States.

Since the German government had repeatedly claimed to be unaware of the presence of American nationals on board Lusitania or on her sister ship Britannic at the time that vessel was torpedoed, the British diplomat's revelations seriously damaged U.S.-German relations and inflamed anti-German sentiments among the American public -- particularly in northern New England and in Louisiana, both of which were home to substantial numbers of people with cultural and ancestral ties to Germany's arch-nemesis France. In later years historians would cite this meeting as one of the tipping points in the chain of events that subsequently led Wilson to reverse his previous neutralist stance and declare war on Germany.A new article by Chris Oakley

Two other incidents, which happened during Wilson's 1916 re-election campaign, would further influence his decision to abandon neutrality in the First World War: the discovery of a plot by German spies to blow up a U.S. munitions factory in New Jersey and the interception of a German diplomatic telegram in which Berlin promised to help Mexico re-conquer its former Southwestern territories from the United States in return for Mexican support of Germany in its conflict with the Allied powers. The telegram in particular turned out to be the last straw for the President, who broke off diplomatic relations between the U.S. and Germany two days after it was discovered.