In a skillet over medium heat, brown the ground beef with the chopped onion until the beef is cooked through and the onions are translucent. Drain any excess grease.

Transfer the cooked beef and onions to a slow cooker.

Add the black beans, pinto beans, corn, tomato sauce, diced tomatoes with green chilies, taco seasoning, and beef broth to the slow cooker.

Stir all ingredients until well combined.

Set the slow cooker to low and cook for 8 hours, allowing the flavors to meld together.

Serve the soup hot, with optional toppings such as shredded cheese, sour cream, and crushed tortilla chips if desired.