Combine olive oil, red onion, garlic, cumin, salt, cinnamon, black pepper, and allspice in a large pot over medium-low heat; cook and stir until onion and garlic are browned, about 5 minutes.
Combine 2 cups vegetable broth, black beans, and tomatoes in a blender; puree until smooth.
Pour remaining 2 cups vegetable broth, pureed black bean mixture, and pumpkin puree into the pot. Simmer soup, uncovered, until thick, 40 to 45 minutes. Stir in balsamic vinegar before serving.
