Final answer:
The driving force behind the global expansion of capitalism in the twenty-first century is the circulation of capital. Therefore, the correct option is b. the circulation of capital.
Step-by-step explanation:
The driving force behind the global expansion of capitalism in the twenty-first century is the circulation of capital. The movement toward globalization and trade liberalization has resulted in a tremendous increase in capital mobility, which has shifted domestic politics and favored capitalists with mobile assets. This trend tends to favor the mobile capital owners over workers.