What are the purposes of transnational corporations?

The purpose of a transnational corporation is to maximize profits through horizontal expansion across international borders. As certain businesses grow, they eventually reach the extent of their profitability within the borders of the nation in which they are headquartered. The owners of such companies will, if they determine that a market for their goods and/or services exists in other countries, establish what are known as "foreign subsidiaries" in those other countries. Especially when the issue is a major trade partner—in the case of the United States, major trade partners could include Canada, the European Union, China and Japan—the incentive to establish operations in those countries is enormous.
Another major purpose of a transnational corporation is to circumvent the regulatory and/or tax structures of one's native country. If corporate tax rates and regulatory structures are less imposing than in one's home country, the corporation's officers will often establish foreign subsidiaries to decrease those tax and regulatory burdens for at least a portion of the company's business.
Establishing a foreign subsidiary in a country with which a particular corporation maintains a strong relationship is an important way of influencing the decisions of the foreign government. By operating a manufacturing facility or financial institution in a foreign country, especially one that employs many local workers and contributes to the local economy's tax base, the transnational corporation can wield substantially more influence in the decision-making processes of local, provincial, and national governments.