Poland Lightning War

The background of the story is set in World War I, when Germany was defeated. After Hitler came to power, he reorganized his armaments at a very fast speed and took Poland as the primary attack target. Although Poland was promised by Britain and France to maintain the integrity of Poland’s territory, the German army entered Poland smoothly due to the “concession” after the negotiations between Germany and the Soviet Union. The territory, and won a lightning-fast victory, and later historians have dubbed it a successful example of "blitzkrieg".

—description from the publisher (translated)