Brown the ground beef with the diced yellow onion and minced garlic in a skillet over medium-high heat until no longer pink. Drain excess fat.
Transfer the browned beef mixture to the slow cooker.
Add the kidney beans, tomato sauce, diced tomatoes, beef broth, chili powder, cumin, salt, and black pepper. Stir well to combine.
Cover and cook on Low for 6-8 hours, or on High for 3-4 hours, until flavors are well combined.
Serve hot, garnished with shredded cheddar cheese, sour cream, diced red onion, cilantro, and tortilla chips.