Karen's Chili Con Carne Soup

Heat oil in a stockpot over medium heat. Add onions and garlic; cook and stir until tender, about 5 minutes. Add ground beef; cook and stir until browned and crumbly, 5 to 7 minutes. Mix in tomatoes, navy beans, chili beans, black beans, green bell pepper, celery, brown sugar, vinegar, chili powder, and salt. Bring to a boil. Reduce heat to medium-low and let simmer until thick, at least 1 hour.