Written By: Ben Cosgrove

On Sept. 1, 1939, one week after Nazi Germany and the Soviet Union signed a non-aggression pact, more than a million German troops, along with 50,000 Slovakian soldiers, invaded Poland. Two weeks later, a half-million Russian troops attacked Poland from the east. After years of vague rumblings, explicit threats and open conjecture about the likelihood of a global conflict in Europe, the Pacific and beyond the Second World War had begun.

The ostensible aim of Germany’s unprovoked assault, as publicly stated by Hitler and other prominent Nazi officials, was the pursuit of lebensraum that is, territory deemed necessary for the expansion and survival of the Reich. But, of course, Hitler had no intention of ending his aggression at Poland’s borders, and instead was launching a full-blown war against all of Europe. (On Sept. 3, both England and France declared war on Germany but not on the USSR.)

The invasion during which German troops, especially, drew virtually no distinction between civilians and military personnel and routinely attacked unarmed men, women and children lasted just over a month. Caught between two massive, well-armed powers, the Polish army and its Air Force fought valiantly (contrary to legend, which has the Poles surrendering quickly, with barely a whimper). In the end, Poland’s soldiers and aviators, fighting on two fronts, were simply overwhelmed.

In the weeks and months after the invasion, a German photographer named Hugo Jaeger traveled extensively throughout the vanquished country, making color pictures of the chaos and destruction that the five-week battle left in its wake. Here, LIFE.com presents a series of Jaeger’s pictures from Poland: portraits of a country subjugated not by one enemy, but by several. There 

IJaeger’s photos include chilling images of evil–Hitler and other Nazis—and we see early, unsettling evidence of the violence, unprecedented in its scope, that would soon be visited upon scores of countries and countless people.

Refugees near Warsaw during the 1939 German invasion of Poland. (Sign reads, 'Danger Zone -- Do Not Proceed.')

Refugees near Warsaw during the 1939 German invasion of Poland. (Sign reads, ‘Danger Zone — Do Not Proceed.’)

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Burned-out tank, Warsaw, 1939.

Burned-out tank, Warsaw, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Adolf Hitler (right) prepares to fly to the Polish front, 1939.

Adolf Hitler (right) prepares to fly to the Polish front, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Post-invasion Poland, 1939.

Post-invasion Poland, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Unfinished Polish bombers, 1939.

Unfinished Polish bombers, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Near Sochaczew during the German invasion of Poland, 1939.

Near Sochaczew during the German invasion of Poland, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Polish soldiers captured by Germans during the invasion of Poland, 1939.

Polish soldiers captured by Germans during the invasion of Poland, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Polish soldiers and a Red Cross nurse captured during the invasion of Poland, 1939.

Polish soldiers and a Red Cross nurse captured during the invasion of Poland, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Captured Polish soldiers, 1939.

Captured Polish soldiers, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

German troops prepare for victory parade after the invasion of Poland, 1939.

German troops prepare for victory parade after the invasion of Poland, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

German victory parade in Warsaw after the invasion of Poland, 1939. (Hitler is on platform, arm raised in Nazi salute.)

German victory parade in Warsaw after the invasion of Poland, 1939. (Hitler is on platform, arm raised in Nazi salute.)

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Adolf Hitler views victory parade in Warsaw after the German invasion of Poland, 1939.

Adolf Hitler views victory parade in Warsaw after the German invasion of Poland, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Right to left, front row: Adjutant Wilhelm Brueckner, Luftwaffe fighter ace Adolf Galland, Gen. Albert Kesselring and Gen. Johannes Blaskowitz view the victory parade in Warsaw after the German invasion of Poland, 1939.

Right to left, front row: Adjutant Wilhelm Brueckner, Luftwaffe fighter ace Adolf Galland, Gen. Albert Kesselring and Gen. Johannes Blaskowitz view the victory parade in Warsaw after the German invasion of Poland, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Head of the SS Heinrich Himmler (right), one of the chief architects of the Holocaust, speaks with an unidentified officer in Warsaw after German invasion of Poland, 1939.

Head of the SS Heinrich Himmler (right), one of the chief architects of the Holocaust, speaks with an unidentified officer in Warsaw after German invasion of Poland, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Warsaw citizens buried their dead in parks and streets after the invasion of Poland, 1939.

Warsaw citizens buried their dead in parks and streets after the invasion of Poland, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Warsaw citizens buried their dead in parks and streets after the invasion of Poland, 1939.

Warsaw citizens buried their dead in parks and streets after the invasion of Poland, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Street scene following the German invasion of Poland, 1939.

Street scene following the German invasion of Poland, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

German nationals prepare for repatriation during the invasion of Poland, 1939.

German nationals prepare for repatriation during the invasion of Poland, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Polish farmers and peasants flee German military during invasion of their country, 1939.

Polish farmers and peasants flee German military during invasion of their country, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Polish women clean captured Polish guns in Modlin Fortress, north of Warsaw, 1939.

Polish women clean captured Polish guns in Modlin Fortress, north of Warsaw, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Jewish women and children in Gostynin, Poland, after the German invasion, 1939.

Jewish women and children in Gostynin, Poland, after the German invasion, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Polish refugees, Warsaw, 1939.

Polish refugees, Warsaw, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Warsaw, 1939.

Warsaw, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Near Modlin Fortress, Poland, 1939.

Near Modlin Fortress, Poland, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Near Modlin Fortress, Poland, 1939.

Near Modlin Fortress, Poland, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Scene in post-invasion Poland, 1939.

Scene in post-invasion Poland, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Poles stand beneath monument to Polish patriot, Jan Kilinski, 1939.

Poles stand beneath monument to Polish patriot, Jan Kilinski, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Near Sochaczew during the German invasion of Poland, 1939.

Near Sochaczew during the German invasion of Poland, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Near Danzig after the German conquest of Poland, 1939.

Near Danzig after the German conquest of Poland, 1939.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Flea market in post-invasion Warsaw Ghetto, 1940.

Flea market in post-invasion Warsaw Ghetto, 1940.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

Near Warsaw, fall 1939; sign points to the battle front.

Near Warsaw, fall 1939; sign points to the battle front.

Hugo Jaeger—The LIFE Picture Collection/Getty Images

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