Cook ground beef in a large skillet over medium-high heat until browned and crumbly, 5 to 7 minutes; drain and discard grease.

Transfer beef to a slow cooker. Add tomato sauce, diced tomatoes, onion, jalapeño peppers, chili powder, cayenne pepper, salt, garlic, and black pepper; stir to combine. Cook on Low for 10 hours or High for 6 1/2 hours.