4 (10 ounce) cans diced tomatoes with green chile peppers
3 cloves garlic
or more to taste
5 (15 ounce) cans pinto beans
drained and rinsed
2 tablespoons red pepper flakes
1 tablespoon salt
1 tablespoon dried sage
1 ½ teaspoons fennel seeds
1 teaspoon ground cumin
Place bacon in a large skillet and cook over medium-high heat, turning occasionally, until crispy, about 7 minutes. Drain bacon slices on paper towels; retain grease in the skillet.
Heat olive oil in a large pot over medium heat. Add ground buffalo and vinegar. Cook and stir until browned, 5 to 7 minutes. Add the bacon.
Put onions in the skillet with the reserved bacon grease. Cook patiently over medium-low heat until deeply browned, 20 to 30 minutes.
Stir crushed tomatoes, diced tomatoes, and garlic cloves into the pot with the buffalo and bacon. Add the browned onions, pinto beans, red pepper flakes, salt, sage, fennel seeds, and cumin. Stir regularly over low heat until flavors have combined, about 1 hour.