Relations between the USA and Germany are increasingly tense. Germany’s U-boat war against British shipping is the main cause of problems between the two countries. U-boat attacks with no warning on British ships inevitably give rise to American casualties. The sinking of the Lusitania, with much American loss of life, caused outrage in the United States. That led to American protests; eventually the Germans backed down, calling off the U-boats to avoid a rupture with the Americans.
More recently however the German U-boat campaign has been escalated again. The U-boats have been given permission to attack all armed civilian ships of the Allies without warning. As most British and French ships carry arms to protect themselves from surfaced U-boats, this more or less gives the U-boats carte blanche to attack at will. The recent sinking of the Sussex has led to more American casualties (though no fatalities), prompting more American anger at the Germans.
President Wilson has already sent a stern letter of protest to the Germans. Today he addresses Congress, stating that unless the Germans immediately bring an end to its U-boat campaign then he will have no option but to sever diplomatic relations with them. If such were to happen then war between the USA and Germany would soon follow.