1945 marked the end of World War II and the fall of Nazi Germany and the Empire of Japan. It is also the year concentration camps were liberated and the only year in which atomic weapons have been used in combat.
Below, the events of World War II have the "WWII" prefix.
January 1945
January 1 – WWII:
Germany begins Operation Bodenplatte, an attempt by the Luftwaffe to cripple Allied air forces in the Low Countries.
Chenogne massacre: German prisoners are allegedly killed by American forces near the village of Chenogne, Belgium.
January 6 – WWII: A German offensive recaptures Esztergom, Hungary from the Soviets.
January 12 – WWII: The Soviet Union begins the Vistula–Oder Offensive in Eastern Europe, against the German Army.
January 13 – WWII: The Soviet Union begins the East Prussian Offensive, to eliminate German forces in East Prussia.
January 16 – WWII: Adolf Hitler takes residence in the Führerbunker in Berlin.
January 17
WWII: The Soviet Union occupies Warsaw, Poland.
The Holocaust: Swedish diplomat Raoul Wallenberg, who has saved thousands of Jews, is taken into custody by a Soviet patrol during the Siege of Budapest and is never again seen publicly.
January 18 – The Holocaust: The SS begins the evacuation of Auschwitz concentration camp. Nearly 60,000 prisoners, mostly Jews, are forced to march to other locations in Germany; as many as 15,000 die. The 7,000 too sick to move are left without supplies being distributed.
January 19 – The Holocaust: Soviet forces liberate the Łódź Ghetto; only 877 Jews of the initial population of 164,000 remain at this time.
January 20
Franklin D. Roosevelt is sworn in for a fourth term as President of the United States, the only President ever to exceed two terms.
Germany begins the Evacuation of East Prussia.
January 21–22 (night) – At the Grünhagen railroad station, located in East Prussia at this date, two trains, heading for Elbing, collide. At dawn the station is reached by Soviet Army infantry and tanks which destroy the station, killing between 140 and 150 people.