What are the Jackboots in book milkweed?

In the book "Milkweed" by Jerry Spinelli, the Jackboots are a group of fictional Nazi soldiers who occupy the fictional Eastern European town of Riveska during World War II. The Jackboots are a symbol of oppression, fear, and violence. They are responsible for the deaths of many innocent people, including Misha's parents. Misha, who is the main character of the story, sees the Jackboots as inhuman monsters who are devoid of compassion and mercy.