The world wars. Mainly World War II when the United States earned the name the arsenal of democracy. At that time, Americans were beginning to believe that the world NEEDED the USA and that democracy had to spread throughout the globe. This led to the Korean and Vietnam War because American citizens felt obligated to be involved, at least in the beginning.
The document that contains a long list of grievances and complaints against the King of England is known as the Declaration of Independence. There were 18 grievances in total.