Nazi Germany (officially known as the German Reich from 1933 until 1943, and the Greater German Reich from 1943 to 1945) was the German state between 1933 and 1945, when Adolf Hitler and the Nazi Party controlled the country, transforming it into a dictatorship. Under Hitler's rule, Germany quickly became a totalitarian state where nearly all aspects of life were controlled by the government. The Third Reich, meaning "Third Realm" or "Third Empire", alluded to the Nazi claim that Nazi Germany was the successor to the earlier Holy Roman Empire (8001806) and German Empire (18711918). The Third Reich, which Hitler and the Nazis referred to as the Thousand-Year Reich, ended in May 1945 after just 12 years when the Allies defeated Germany, ending World War II in Europe.

On 30 January 1933, Hitler was appointed chancellor of Germany, the head of government, by the president of the Weimar Republic, Paul von Hindenburg, the head of state. On 23 March 1933, the Enabling Act was enacted to give Hitler's government the power to make and enforce laws without the involvement of the Reichstag or president. The Nazi Party then began to eliminate all political opposition and consolidate its power. Hindenburg died on 2 August 1934, and Hitler became dictator of Germany by merging the offices and powers of the chancellery and presidency. A national referendum held 19 August 1934 confirmed Hitler as sole Fhrer (leader) of Germany. All power was centralised in Hitler's person and his word became the highest law. The government was not a coordinated, co-operating body, but a collection of factions struggling for power and Hitler's favour. In the midst of the Great Depression, the Nazis restored economic stability and ended mass unemployment using heavy military spending and a mixed economy. Using deficit spending, the regime undertook a massive secret rearmament program, forming the Wehrmacht (armed forces), and constructed extensive public works projects, including the Autobahnen (motorways). The return to economic stability boosted the regime's popularity.

Racism, Nazi eugenics, and especially antisemitism, were central ideological features of the regime. The Germanic peoples were considered by the Nazis to be the master race, the purest branch of the Aryan race. Discrimination and the persecution of Jews and Romani people began in earnest after the seizure of power. The first concentration camps were established in March 1933. Jews, liberals, socialists, communists, and other political opponents and undesirables were imprisoned, exiled, or murdered. Christian churches and citizens that opposed Hitler's rule were oppressed and many leaders imprisoned. Education focused on racial biology, population policy, and fitness for military service. Career and educational opportunities for women were curtailed. Recreation and tourism were organised via the Strength Through Joy program, and the 1936 Summer Olympics showcased Germany on the international stage. Propaganda Minister Joseph Goebbels made effective use of film, mass rallies, and Hitler's hypnotic oratory to influence public opinion. The government controlled artistic expression, promoting specific art forms and banning or discouraging others.

From the latter half of the 1930s, Nazi Germany made increasingly aggressive territorial demands, threatening war if these were not met. The Saarland voted by plebiscite to rejoin Germany in 1935, and in 1936 Hitler sent troops into the Rhineland, which had been demilitarized after World War I. Germany seized Austria in the Anschluss of 1938, and demanded and received the Sudetenland region of Czechoslovakia in that same year. In March 1939, the Slovak state was proclaimed and became a client state of Germany, and the German Protectorate of Bohemia and Moravia was established on the remainder of the occupied Czech Lands. Shortly after, Germany pressured Lithuania into ceding the Memel Territory. Germany signed a non-aggression pact with the Soviet Union and invaded Poland on 1 September 1939, launching World War II in Europe. By late 1942, Germany and its European allies in the Axis powers controlled much of Europe and North Africa. Extended offices of the Reichskommissariat took control of Nazi-conquered areas and a German administration was established in the remainder of Poland. Germany exploited the raw materials and labour of both its occupied territories and its allies.

Genocide, mass murder, and large-scale forced labour became hallmarks of the regime. Starting in 1939, hundreds of thousands of German citizens with mental or physical disabilities were murdered in hospitals and asylums. Einsatzgruppen paramilitary death squads accompanied the German armed forces inside the occupied territories and conducted the genocide of millions of Jews and other Holocaust victims. After 1941, millions of others were imprisoned, worked to death, or murdered in Nazi concentration camps and extermination camps. This genocide is known as the Holocaust.

While the German invasion of the Soviet Union in 1941 was initially successful, the Soviet resurgence and entry of the United States into the war meant that the Wehrmacht lost the initiative on the Eastern Front in 1943 and by late 1944 had been pushed back to the pre-1939 border. Large-scale aerial bombing of Germany escalated in 1944 and the Axis powers were driven back in Eastern and Southern Europe. After the Allied invasion of France, Germany was conquered by the Soviet Union from the east and the other Allies from the west, and capitulated on 8 May 1945. Hitler's refusal to admit defeat led to massive destruction of German infrastructure and additional war-related deaths in the closing months of the war. The victorious Allies initiated a policy of denazification and put many of the surviving Nazi leadership on trial for war crimes at the Nuremberg trials.

The Battle of the Bulge, also known as the Ardennes Offensive, was a major German offensive campaign on the Western Front during World War II which took place from 16 December 1944 to 25 January 1945. It was launched through the densely forested Ardennes region between Belgium and Luxembourg towards the end of the war in Europe. The offensive was intended to stop Allied use of the Belgian port of Antwerp and to split the Allied lines, allowing the Germans to encircle and destroy the four Allied forces and cause the Allies to negotiate a peace treaty in the Axis powers' favor. The Battle of the Bulge remains among the most important battles of the war, as it marked the last major offensive attempted by the Axis Powers on the Western front. After their defeat, Germany would retreat for the remainder of the war.

The Germans achieved a total surprise attack on the morning of 16 December 1944, due to a combination of Allied overconfidence, preoccupation with Allied offensive plans, and poor aerial reconnaissance due to bad weather. American forces bore the brunt of the attack. The Germans had attacked a weakly defended section of the Allied line, taking advantage of heavily overcast weather conditions that grounded the Allies' superior air forces. Fierce American resistance on the northern shoulder of the offensive, around Elsenborn Ridge, and in the south, around Bastogne, blocked German access to key roads to the northwest and west that they counted on for success. Columns of armor and infantry that were supposed to advance along parallel routes found themselves on the same roads. This congestion, and terrain that favored the defenders, threw the German advance behind schedule and allowed the Allies to reinforce the thinly placed troops. The farthest west the offensive reached was the village of Foy-Nôtre-Dame, south east of Dinant, being stopped by the U.S. 2nd Armored Division on 24 December 1944. Improved weather conditions from around 24 December permitted air attacks on German forces and supply lines, which sealed the failure of the offensive. On 26 December the lead element of Patton's U.S. Third Army reached Bastogne from the south, ending the siege. Although the offensive was effectively broken by 27 December, when the trapped units of 2nd Panzer Division made two break-out attempts with only partial success, the battle continued for another month before the front line was effectively restored to its position prior to the attack. In the wake of the defeat, many experienced German units were out of men and equipment, and the survivors retreated to the Siegfried Line.

The Germans' initial attack involved 410,000 men; just over 1,400 tanks, tank destroyers, and assault guns; 2,600 artillery pieces; and over 1,000 combat aircraft, as well as large numbers of other armored fighting vehicles (AFVs). These were reinforced a couple of weeks later, bringing the offensive's total strength to around 450,000 troops, and 1,500 tanks and assault guns. Between 63,222 and 98,000 of these men were killed, missing, wounded in action, or captured. The battle severely depleted Germany's armored forces, which remained largely unreplaced throughout the remainder of the war. German Luftwaffe personnel, and later also Luftwaffe aircraft (in the concluding stages of the engagement) also sustained heavy losses.

From among the Americans' peak strength of 610,000 troops, there were 89,000 casualties, including about 19,000 killed. The "Bulge" was the largest and bloodiest single battle fought by the United States in World War II and the third-deadliest campaign in American history.