In order to execute imperialism, it is very important to have the support of the people. The most efficient way to have and maintain the support of the people is to promote nationalism.
Explanation:
Nationalism is very different than patriotism. Patriotism can be define as the love of being from a country with respecting also the sovereignty of other nations. On the other hand, nationalism is an aggressive love for a country without considering the sovereignty of other nations. Nationalism is the key element to go to war. The leader of a nation can never go to war without practicing nationalism on his people as his political tool.
The United States should guarantee to every State in this Union a Republican Form of Government, they shall also protect each of them against Invasion; and on Application of the Legislature, of the Executive when the Legislature cannot be convened against domestic Violence.