Imperialism happens when a state tries to extend its influence through annexation or achieving commercial or cultural superiority over a region. Throughout history, the state has often been the leader in imperialistic efforts as a strong state has the economic and military means needed to take over another territory.
During the nineteenth century, states had various reasons for imperialism. One of the primary goals was economic. The Industrial Revolution led to states needing new sources of raw materials. European states looked to untapped mineral resources in Africa and Asia in order to feed their growing industrial bases. The leaders of these states then claimed that the indigenous people of these regions were not using them properly; therefore, it took Europeans (and eventually Americans) to utilize these resources. After Mahan's work on the influence of seapower in history, states looked to colonize various islands in the Pacific in order to have coaling stations for their ships. A strong naval fleet was considered vital to protect the shipping lanes of a country in both peace and war.
States also looked at imperialism as a source of nationalistic pride. Germany, a state after 1871, looked at overseas expansion as a source of pride for the new nation. Millions had immigrated from Germany to the New World during the 1800's; it was hoped that new colonies in Africa and the Pacific would allow German settlers to travel abroad and yet still contribute to the mother country. When this failed to materialize as Germans could not be convinced to move to Africa in large numbers, the German leadership stated that colonies were the status symbol of all the "great powers" of Europe. It was a source of pride for Britain to state that "the sun never set on the British Empire."
States also looked at imperialism as competition. It was perceived that if one nation did not colonize, then another nation would. The United States reluctantly got into imperialistic ventures in the Pacific due to fear that Japan and Germany would colonize vital ports in Hawaii and the Philippines. In times of war, it was perceived that colonial troops could also be called upon to join the armies of the mother country. Thousands of Africans and Indians fought for Britain and France in WWI. While it is doubtful that colonial troops helped to turn the tide against the Central Powers, the pro-imperialism politicians could point to the added manpower as part of their argument that their nations needed colonies.