It was a sad day but a good day.

Congress had declared war on Japan and the defense of America was underway.

The day before, of course, Japan had launched an extraordinary attack on Pearl Harbor. More than 2,400 Americans were dying or dead, four battleships were sunk, nearly 200 aircraft were destroyed, and many other warships were damaged.

But for Britain, the attack on Pearl Harbor was a solemn salvation.

In his third volume of The Second World War, Churchill notes his relief that America would join the fight against Axis fascism: "United we could subdue everybody else in the world. Many disasters, immeasurable cost and tribulation lay ahead, but there was no more doubt about the end."

Describing "silly people" who doubted American industrial and human power, Churchill explained that he "had studied the American Civil War, fought out to the last desperate inch. American blood flowed in my veins. I thought of a remark which Edward Grey [a former British Ambassador to Washington] had made to me more than thirty years before — that the United States is like 'a gigantic boiler. Once the fire is lighted under it there is no limit to the power it can generate.' Being saturated and satiated with emotion and sensation, I went to bed and slept the sleep of the saved and thankful."

Announcing Britain's declaration of war on Japan, also today 76 years ago, Churchill told the British people that Japan and Germany were part of the same breed: "When we think of the insane ambition and insatiable appetite, which have caused this vast, melancholy extension of the war, we can only feel that Hitler's madness has infected the Japanese minds and that the root of the evil and its branch must be extirpated together."

Churchill's purpose here was to align popular expectations with the need to counter the Axis across the world. It meant another pressure point for the already weary British psyche, but Churchill gave Britons comfort: Finally, they were no longer alone. When Nazi Germany declared war on the United States just three days later, Churchill must have had a good many glasses of champagne!

Still, ever the strategist, Churchill knew he had to consolidate the American political establishment around his agenda of prioritizing Hitler's defeat.

Heading to Washington, Churchill gave a masterful speech to Congress on December 26, 1941. As he stood in the House of Representatives, Churchill began with humor, referencing his mother's American citizenship. "By the way," he said, "I cannot help reflecting that if my father had been American and my mother British instead of the other way around, I might have got here on my own!"

But recognizing the still visceral anger of the American public less than three weeks after Pearl Harbor, Churchill threw scorn on Japan's leaders. They were insane for attacking the United States, the Prime Minister explained, "It becomes still more difficult to reconcile Japanese action with prudence or even with sanity. What kind of a people do they think we are?" Churchill roared, "Is it possible that they do not realize that we shall never cease to persevere against them until they have been taught a lesson which they and the world will never forget!?"

Congress loved it and the alliance was secured.

Eighteen months later, U.S. and British forces found victory in their first ground offensive of the war, driving Axis forces out of North Africa.

A year later, allied forces would land in France.

A month after that, Japanese forces were driven from Guam.

A month after that, Patton's Third Army was chasing the Wehrmacht into Germany.

Nine months after that, Germany had surrendered.

Three months after that, Japan saw the light and followed suit.

The war was won.