On the 29th of December, 1940, FDR gave one of his many radio addresses, in which he used the now famous phrase "arsenal of democracy," saying the United States would supply Britain with whatever war supplies they would need to resist Hitler, whose Blitzkrieg (lightning war) had easily defeated France, leaving the entire continent of Europe occupied by fascist forces.

Looking ahead to the coming year, FDR began to prepare the United States citizens for the very real possibility of war. Knowing many were still squeamish about international military involvement following WWI, he couldn't just slap the reality of the situation down of the table like a raw piece of meat. Instead, he had to feed it to people in small bits.

If this analogy is starting to get kind of gross, well, war is gross, so get over it. Basically, FDR broke it to them gently, and "arsenal of democracy" was an early step in this process.

By referring to the U.S. with this famous phrase, FDR did two important things to advance his quiet campaign for crumbling isolationism. The first was that he identified the country as a major world power and the forceful leader of the free world. The second was that he characterized the U.S. as the protector of democracy itself—an idea he would return to in depth during this State of the Union address a month later, a speech known for its presentation of the "Four Freedoms."

Lend-Lease is the outcome, in the form of foreign policy, of the foundation political work done by FDR in the "Arsenal of Democracy" radio broadcast, which can be considered an early step in his preemptive measures of defense against the Axis powers of WWII.