The United States was, in many ways, unprecedented: prior to its creation, democracy on such a scale was seen as untried and unproven. The Framers of the Constitution were aware of the challenges they were facing—in fact, it should be noted that the first attempt at forming a governing structure...
for the United States, as represented by the Articles of Confederation, had actually proved unsatisfactory; it was abandoned in favor of the Constitution.
The first ten amendments were added in the context of the Federalist Debates, which were waged over the ratification of the US Constitution. Among the charges levied by the anti-Federalists was that too much power had been concentrated in the federal government and that the Constitution furthermore lacked a Bill of Rights (which would serve as a guarantor of civil liberties). Thus, the first ten amendments served to correct this oversight, drawing from American influences, such as the Virginia Declaration of Rights, as well as older European examples, such as the English Bill of Rights.
Additionally, the ideas and protections that can be found in the Bill of Rights should be understood as reflecting concerns from the Enlightenment Era about absolutism: to give one example, the First Amendment aims to prevent government censorship (both of free speech and the press) while also guaranteeing freedom of religion (thus preventing the rise of State Churches and the intertwining of religion and state power seen back in Europe).
As the country would continue to evolve over time, later amendments would reflect dramatic transformations and turning points. This can be seen in examples such as the Reconstruction Era amendments that followed the Civil War (ending slavery and granting citizenship and voting rights to African Americans), as well as the Progressive Era amendments of the early twentieth century, which saw the introduction of the income tax (sixteenth amendment), the direct election of senators (seventeenth amendment), and the success of the women's suffrage movement (nineteenth amendment).