How did the united states contribute to the second world war prior to officially declaring war?

Provide arms and ships to friendly European nations fighting Germany.

Explanation:

The public opinion in the United States about the world war second was that they called it War of Europe. Therefore it was not possible for president Roosevelt to openly support either side. But he remained inclined towards the Allies cause against Nazi Germany and this was reflected in the program of Land Lease by which United States supplies war materials to Britain on the condition of getting a 99-year lease land in Newfoundland and the Caribbean.