To provide a greater certainty that the observed results are not by chance.
For most of the American history, the isolationist tendency prevailed in its foreign policy. In its early years, American foreign policy was in fact a reflection of the American national interest, namely to fortify the new nation’s independence. With the European continent torn apart by the great powers’ rivalry, the American nation could develop at its own pace, without any major external threat. Therefore the nonalignment practice, the isolationism, the constant effort to remain free of entanglements overseas became characteristic features of the early American foreign policy (Kissinger, 10-12). The step forward in strengthening this view was made in 1823, when the Monroe Doctrine was proclaimed, a political decision basically stating that further European action on the American continent will be interpreted as an intervention and a threat for the new nation’s stability. Surprisingly accepted without much of a revolt by the European powers, the new doctrine defended America and assured an uninterrupted pursue of its goal: growing internally and turning itself into a Great Power, with the formidable advantage of not being threatened by state rivalry
There were 13 new states added from 1791 to 1838, for a total of 26. 2. Five new states—Louisiana, Indiana, Mississippi, Illinois, and Alabama—were admitted during the 1810s, the most of any decade.
You're answer is going to be C
