What is the main conflict in The Tin Drum by Gunter Grass?

The Tin Drum is a fable of the mythical and diminutive Oskar Matzerath's life in the free city of Danzig, Germany during World War II. Oskar is a mythical figure, perfectly cognizant from the moment he is born. At his birth, Oskar's mother announces that at the age of three he will be given a drum. His father proclaims that at maturity, Oskar will inherit the family business, a small grocery shop. At that very moment, Oskar determines never to grow to maturity, but to stop growing after receiving the drum on his third birthday. The drum becomes Oskar's solace and his favorite method of communication. The novel follows Oskar's experiences during the war, defending a Polish post office against the Germans, and later entertaining the German soldiers with a troupe of dwarfs.