Final answer:
The most important barriers to global flows are constructed by nation-states and corporations. Nation-states have the authority to create and enforce laws, regulations, and trade policies, while corporations shape global flows through their economic influence and activities.
Step-by-step explanation:
The most important and obvious barriers to global flows are constructed by nation states. Nation states have the authority to create and enforce laws, regulations, and trade policies that can hinder or restrict the movement of goods, services, and people across borders. For example, governments often impose tariffs, quotas, and other trade barriers to protect domestic industries from foreign competition.
Another barrier to global flows is corporations. While corporations are not typically responsible for creating laws or policies, they can shape global flows through their economic influence and activities. Global corporations often prioritize their own interests, such as maximizing profits, which can lead to negative consequences for local communities and hinder the free flow of goods, services, and capital.