Manifest Destiny was a phrase first coined by John L. O"Sullivan, a Democratic editor, referring to the fact that he believed it was the United States" duty to expand over the entire continent, and develop all the land for the rapidly growing population. This idea could be traced back to the "city on a hill" idea, thought of by the Puritans. The phrase encompassed physical, social and political ideology. The establishment of democracy and suffrage with no king or national church was an idea uplifted by many. Numerous Americans also believed their system to be superior to every other economical system, and thought that it should be implemented worldwide. This is not to say that Manifest Destiny was only a great social plan. It also had its personal interests. Business owners recognized the great opportunities the Pacific coast presented, foreseeing smoother trade with Asia through good harbors.
I believe that the idea of manifest destiny has changed over the years in many ways, but the idea has not really receded, just split up. No longer is it one idea upheld by the majority of Americans, but many ideas that groups work to promote. These could also be viewed as reform movements. Politicians see it as their manifest destiny to further their view of society structure over the world. Christians and other religions believe their manifest destiny is to spread their religion throughout the earth.
Manifest destiny has indeed affected our country (and the rest of the world) in many ways. If it had not been a goal of Americans back then to expand over the rest of the continent, we would possibly not have many of the established states and territories we do today. If businesses had not opened new locations, the established trade routes and ports we have might not exist. And of course, if politicians and other leaders had not spread our concept of freedom, America may easily have fallen into another form of leadership.