I am not sure but I think it’s a
"without warning"-- this repeated statement gives the speech impact.
FDR's fireside chat repeats the phrase "without warning" to remind the citizens that the Axis powers have been ruthless. He suggests the Axis powers have created a pattern of surprise attacks demonstrating their evil methods. This creates a clear line between the sides and puts the US on a side of morality.
If it’s the first world war this was due to the unrestricted submarine ware fair where the Germans sunk any ships or submarines in one of the oceans. Warning Germany not to sink American ships Germany did and America declared war on Germany. If you are talking about world war 2 then that is due to the Japanese booming Pearl Harbor but missing a flight carrier.
Answer: IT CHANGED THE WORLD
Explanation: WORLD WAR II HAPPENED SO THAT'S HOW IT CHANGED THE WORLD
