This is a good question. There are several important reasons why Calvinism is important to the history of America.
First, many of the people who came over from Europe to settle in America were Protestant Christians. More specifically, they were Calvinists. They followed the theology that emerged from John Calvin. For example, the Puritans were Calvinist. In addition, the Dutch Reformed church was also Calvinistic in their theology. So, to know our first ancestors, we need to know something about their religious beliefs.
Second, we can say that Calvinism breeds a certain type of lifestyle. Calvinists believed in a strong work ethic. Weber, the great sociologist, even made a correlation between Calvinism and Capitalism. His point was that Calvinists worked hard and saved and invested. There was a theological sentence that encapsulated this idea:
"Laborare est Orare." "To work is to pray."
Third, some of the greatest minds of early America were Calvinists as well. Two of the most famous people of early American history were Cotton Mather and Jonathan Edwards. They were both Calvinists. So, to some degree, American sensibility even today is Calvinistic.