Acquiring more physical space for what he considered Germany's pure Aryan race was Adolf Hitler's impetus for starting World War II. Though Germany eventually lost, Hitler's expansionist policy led the Nazi military to invade more than 10 countries during the first two years of the war. Germany overwhelmed the opposition with unprecedented force involving tanks, heavy artillery and aircraft that became known as blitzkrieg, or "lightning war."

First Target: Poland

Hitler had long set his sights on Poland, which received several German provinces under the Treaty of Versailles after World War I. He first convinced Soviet leader Joseph Stalin to enter into the German-Soviet Non-Aggression Pact, which assured Hitler no Soviet resistance in his invasion of Poland. Both parties agreed to divide Polish lands between them. In September 1939, Nazi Germany unleashed its initial blitzkrieg on Poland, which surrendered weeks later. Great Britain and France, which along with the Soviet Union and the U.S. would come to be known as the Allied Powers, pledged military support to Poland and declared war on Germany.

Scandinavia, a Strategic Conquest

In April 1940, Germany launched simultaneous attacks on Denmark and Norway. Denmark, which was easily defeated, was a stepping stone to Norway, which lay along Germany's iron supply route from Sweden and was useful as a base from which to strike Great Britain. Some German army groups attacked major Norwegian ports; others descended on the country's airfields by parachute. British and Norwegian troops mounted a formidable resistance for several weeks. The German invasion of Scandinavia succeeded, however, because Britain was forced to attend to a dire situation in France.

Attack on Western Europe

Germany's offensive in Western Europe began in May 1940 with blitzkrieg assaults on the Netherlands, Belgium and Luxembourg. Simultaneously, German armies invaded France. As France anticipated, the Nazis sent armies through central Belgium and to the Maginot Line, a heavy series of fortifications that spanned the border with Germany. The most powerful German contingent, however, entered through the Ardennes Forest, which the French considered impassable to tanks and, therefore, left unprotected. In June, the Nazis captured Paris, and France signed an armistice agreement with Germany.

Coercion in the Balkans

Hitler sought to establish a front in Eastern Europe for an invasion of the Soviet Union. From 1940 to 1941, Germany took advantage of territorial conflicts among Hungary, Romania, Slovakia, Bulgaria and Yugoslavia -- and their shared fear of Soviet aggression -- to coerce the Balkan countries into the Tripartite Pact it had signed with Italy and Japan; the Axis powers. Nazi troops invaded Romania, prized for its oil fields, in October 1940, and would occupy Hungary, Slovakia, and Bulgaria and dissolve the Yugoslav state. Germany invaded Yugoslavia in April 1941 while simultaneously attacking -- and eventually occupying -- a British-backed Greece, which had successfully fended off an Italian offensive.

An Agreement Broken

Hitler breached the German-Soviet Non-Aggression Pact in June 1941 when he invaded the Soviet Union. Three million Nazi troops and some 3,000 tanks and 2,500 aircraft -- the most powerful invasion ever mounted -- entered Soviet territory. The attack took Stalin's Red Army by surprise, allowing the Nazis to make significant inroads. Aided by the harsh Russian winter, for which Hitler's men were unprepared, the Soviets halted the Germans, who just fell short of reaching Moscow. A key turning point in favor of the Allies was the Battle of Stalingrad. Between July 1942 and February 1943, German and Soviet forces struggled for control of Stalin's namesake city; the latter prevailed.