Introduction The concept of aggressive expansion sometimes also, somewhat ironically, called American imperialism is recognized as a 19th century phenomenon by most historians. However, some attribute its beginning to the first colonization of the North American continent. For example, the historian Paul Kennedy wrote; “From the time the first settlers came to Virginia from England and began moving westward, this was an imperial nation, a conquering nation.” (P. Kennedy, 2002) This means that western expansion should also be considered an act of aggressive expansion which makes sense considering that the territory was already inhabited by Native Americans. While it is true that early US foreign policy was portrayed as isolationist in its behavior towards other recognized nations, the reason for this is the view of Western expansion as a discovery, not a conquest. This is due to the cultural difference, particularly the concept of land ownership, between the Indians and the white settlers. This “exploration” is the main reason for the subsequent changes and cultural acceptance of aggressive expansion; of course there were other contributing factors, such as Manifest Destiny, the Louisiana Purchase, and the development of nationalism, which will be explored in the next part of this essay. The terms presented are often used as an argument to explain the American cultural mentality in the 19th century and its continuing tradition. Although the concept of conquest is still present even in the United States today, it was a partial failure in the 19th century. This article will analyze the individual cultural concepts that developed in this period of time and answer what was the cause of its failure and what the consequences were. Development of the Aggr concept...... half of the document.... .. the expansion was determined by the need for new territories which arises from one of the fundamental principles of the country, the need for improvement and simple economic necessity to expand. The contributing factors were the presented cultural phenomena that developed with Western expansion. It can be argued that the reason for its partial failure was the internal struggle between the slave and free states and that this situation reached its conclusion in the civil war. Further consequences are the influence on today's foreign policy of the United States and the formation of the image of the United States both in the world and towards its citizens. “Success is someone else's failure. Success is the American Dream that we can continue to dream because most people in most places, including thirty million of us, live wide awake in the terrible reality of poverty.” (Ursula K. LeGuin, 1983)