In a large pot or Dutch oven, brown the Italian sausage over medium heat. Drain off any excess grease.
Add the chopped onion and minced garlic to the pot and cook until softened, about 5 minutes.
Add the shredded cabbage, grated beets, crushed tomatoes, beef broth, thyme, and oregano to the pot. Bring to a boil, then reduce heat and simmer for at least 150 minutes, or until the cabbage and beets are tender.