Heat 3 tablespoons oil in a soup pot over medium-high heat. Add sausage; cook and stir until beginning to brown. Add carrots and cook for 2 minutes. Add garlic; cook for 1 minute more. Add 4 cups chicken broth and 2 teaspoons salt. Reduce heat to a simmer; add black beans, kidney beans, great Northern beans, and bell pepper. Continue to simmer for 1 hour.

Meanwhile, bring remaining 4 cups chicken broth to a boil in a saucepan. Add potatoes and simmer until easily pierced with a fork, about 20 minutes.

At the same time, heat remaining 3 tablespoons vegetable oil in a nonstick skillet or saute pan over medium-high heat. Add corn, onion, harissa, remaining 1 teaspoon salt, and black pepper. Saute until they have a few brown spots and a nice flavor, 5 to 7 minutes. Remove from heat.

Place potatoes with chicken broth and corn mixture carefully into an electric blender and blend until smooth, or desired consistency (or leave some out to be left whole). Stir mixture into the soup pot to combine. Turn off heat and add balsamic vinegar. Stir again to combine. Adjust seasonings to taste.