On the issue of liberal ideas, etc., the United States was the first country to be founded on the liberal ideas of John Locke and other philosophers of the Enlightenment, with no monarchy, no hereditary aristocracy and no established religion.
The Bill of Rights guarantees every citizen the freedoms advocated by the liberal philosophers — equality under the law, freedom of religion, freedom of speech, freedom of the press, the right to gather in peaceful assembly, the right to petition the government for redress of grievances, and the right to bear arms, among other freedoms and rights.
In this sense, virtually "all Americans are liberals." However, questions arose before and after the country was founded. In the Dred Scott decision of 1856-57, the Supreme Court ruled that these rights only applied to white men, and that blacks had no rights whatsoever that any white man was obligated to respect. Therefore, the Constitution was amended several times to extend those rights to ever larger classes of all citizens black, brown, etc., in 1868, then specifically to blacks in 1870, to women in 1919, and against the "poll tax" in 1964.
Yes, America is a very liberal founded nation.