Combine chiles, garlic, cumin, oregano, cinnamon, pepper and salt in a large bowl. Add water to cover completely.
Let the chiles sit in water for at least 30 minutes to soften. Then, blend the chiles, garlic, and spices until smooth.
Place the chuck roast in a slow cooker. Pour the blended chili mixture over the beef and add the beef broth. Cook on low for 6 hours or until the beef is very tender.
Shred the beef and return it to the slow cooker. Warm for 15-20 minutes. Serve in warm tortillas, with onion, cilantro, etc.
Notes
Serve with your favorite taco toppings such as onions, cilantro, and salsa.