Final answer:
Max leaves Himmel Street to protect the Hubermanns after Hans draws Nazi attention by giving bread to a Jewish prisoner. His departure is driven by the danger his presence brings to the family during the Holocaust.
Step-by-step explanation:
In The Book Thief, Max Vandenburg leaves Himmel Street because he learns that Hans Hubermann, who has been hiding Max, is likely to be scrutinized by the Nazis after Hans gave bread to a Jewish prisoner being marched through Molching. Max decides to leave to protect the Hubermanns from the dangerous repercussions of being caught harboring a Jew. Due to the growing hostility and scrutiny from Nazi forces, Max's presence in their home puts everyone at risk, and thus he chooses to leave to avoid bringing harm to the family he has come to care for. The broader themes of danger, sacrifice, and the impact of war on individuals are prevalent, reflecting on how external circumstances forced separations and difficult decisions during the Holocaust.