Final answer:
The U.S. has a relationship with Nigeria largely because of oil, with Nigeria being an important part of OPEC and a critical provider of oil to the U.S. to supplement its own production.
Step-by-step explanation:
From the relationship between Nigeria and the U.S., Nigeria provides a critically important resource to the United States, which is oil. The U.S. cannot support its petroleum needs solely through domestic resources, leading to the development of policies aimed at reducing reliance on foreign oil. Nigeria, being one of the members of the Organization of Petroleum Exporting Countries (OPEC), plays a significant role in the global oil market.
U.S. oil companies have been investing in oil development in countries outside the Middle East to diversify sources of oil, and Nigeria has been an important supplier in this context. Historical political issues in countries with oil reserves, like Nigeria in the pre-1990s era, have affected the distribution of oil wealth between the inhabitants and the oil companies/dictatorships.
Figure 2. Sources of United States Net Petroleum Imports, 2009, illustrates that the OPEC countries, including Nigeria, have sizeable control over oil production levels and thus can influence international oil supply and prices.