"Liberalism" as a philosophical tradition begins with the Scottish Enlightenment thinkers Locke, Hume, and particularly Smith, who is considered the first to use the term "liberal" in this context.
Just like how Darwin's observations aboard the HMS Beagle gave him insight into the origin of species, these Scotsmen were trying to make sense of the natural order they saw in flourishing English markets. How were these markets so well-coordinated without any direction from a central authority?
Liberalism was their attempt to work out the processes of natural order - processes that the next two hundred years of economics and political theory would continue to explicate and formalize. The central point of liberalism is that freedom works. Whether it works, how it works, and how well it works are all valid questions. But liberal theory is the theory of how freedom works. It is emphatically NOT a theory of how political majorities can pursue their collective ambitions.
Liberalism as it is used in modern English discourse is a total misnomer. Words change their meanings, fine. But if you don't understand that 18th and 19th century liberalism is virtually the opposite of 20th century liberalism, you will totally misread American history.
Liberals wrote the Constitution, freed the slaves, and invented the market economy on a theory of liberty - both economic and civil. We can pursue an entirely different theory if we want - one that thinks the most important thing to know about markets is their failure; one that imagines we can achieve anything through government if we just elect the right angels; one that thinks majoritarian democracy on every issue is more legitimate than individual choice - we can do that, but let's not call it liberalism, and let's not call its proponents liberals.