Japan
When Pearl Harbor was attacked by Japan on Sunday, December 7, Roger Payne was in Detroit preparing for the first day of his new job on Monday, December 8.
On the 8th, as President Roosevelt was making his famous “day that will live in infamy” speech, and Congress was declaring war on Japan, Roger was on his way back home to enlist as an Air Cadet in the United States Army Air Force, and Japanese forces began invading strategic ports all over Southeast Asia.

The red rectangles on this map indicate when and where those invasions took place..
One of the lesser known – and more interesting – occurrences in 1941, was the first mission of the “Flying Tigers,” a group of US airmen, who, as volunteers rather than US military officers, went to China to help defend the Burma Road from Japanese attacks. The Flying Tigers were supposed to begin their mission in July of the 1941, but circumstances in the area caused a delay until after the Pearl Harbor attack. Their first mission on December 20 was a success and the Flying Tigers became instant heroes, garnering fame and dominating headlines worldwide. Stories of heroic pilots helped add to the prestige of flying and was largely responsible for the surge of young men, like Roger, into the USAAF after Pearl Harbor.
Germany
In June of 1941, five months before Japan attacked Pearl Harbor, Hitler pulled a big double-cross on Russia by attacking them in Poland and continuing eastward with the intention of taking Moscow. It was called Operation Barbarossa. The Moscow offensive began in September, but an especially brutal winter became the major Russian weapon against ill-prepared German troops. Up to 400,000 Germans died from wounds, exposure, and hunger. Nonetheless, Germany had made many gains to the east:

The Battle of the Atlantic, which had begun in 1939, was the German naval offensive to disrupt shipping across the Atlantic to the greatest degree possible. They had largely avoided firing directly on US vessels, but immediately after Pearl Harbor they began laying plans for “Operation Drumbeat,” or, as the German naval commanders preferred to call it, “American Shooting Season.” They would soon be encroaching upon the American coastline with their stealthy and lethal U-boats.
During December Hitler begins talking openly about the idea of removing and exterminating Jews.
The remainder of the month featured one declaration of war after another as the countries of the world decided whether to join the Axis, join the Allies, or stay neutral.
Italy
Italy stayed neutral in the war until Germany defeated France in 1940, and it seemed Germany would surely win the war in Europe. As a result, in mid 1940, Italy joined the Axis and attacked France and Britain in North Africa. All three countries had substantial holdings in Africa:

Italian forces made some gains in the first few months of fighting, but after Indian forces joined with Britain, the tides began to turn, and Italy surrendered in February 1941. Shortly thereafter, Hitler sent the newly organized Afrika Corps to North Africa, under the command of General Erwin Rommel. Rommel dominated for several months, but by December 1941, the Allies were, again, having more success and the fighting was going back-and-forth after the attack on Pearl Harbor.
On the Homefront



Postscript. In the midst of everything else that was happening, on December 26, President Roosevelt signed a bill establishing the fourth Thursday of November as Thanksgiving Day.