February 1941 The Germans send the Afrika Korps to North Africa to reinforce the faltering Italians.

March 1, 1941 Bulgaria joins the Axis.

April 6, 1941–June 1941 Germany, Italy, and Hungary invade Yugoslavia and, together with Bulgaria, dismember it. Yugoslavia surrenders on April 17. Germany and Bulgaria invade Greece in support of the Italians. Resistance in Greece ceases in early June 1941.

April 10, 1941 The leaders of the terrorist Ustaša movement proclaim the so-called Independent State of Croatia. Recognized immediately by Germany and Italy, the new state includes the province of Bosnia-Herzegovina. Croatia joins the Axis powers formally on June 15, 1941.

June 22, 1941–November 1941 Nazi Germany and its Axis partners (except Bulgaria) invade the Soviet Union. Finland, seeking redress for the territorial losses in the armistice concluding the so-called Winter War, agrees to participate in the invasion. The Germans quickly overrun the Baltic states and, joined by the Finns, lay siege to Leningrad (St. Petersburg) by September. In the center, the Germans capture Smolensk in early August and drive on Moscow by October. In the south, German and Romanian troops capture Kiev (Kyiv) in September and capture Rostov on the Don River in November.

December 6, 1941 A Soviet counteroffensive drives the Germans from the Moscow suburbs in chaotic retreat.

December 7, 1941 Japan bombs Pearl Harbor.

December 8, 1941 The United States declares war on Japan, entering World War II. Japanese troops land in the Philippines, French Indochina (Vietnam, Laos, Cambodia), and British Singapore. The Japanese occupy the Philippines, Indochina, and Singapore by April 1942 and take control of Burma in May.

December 11–13, 1941 Nazi Germany and its Axis partners declare war on the United States.