According to Merriam-Webster, liberalism is a "political doctrine that takes protecting and enhancing the freedom of the individual to be the central problem of politics." Note that the technical term "liberalism" is different from the colloquial liberalism vs conservatism idea. In fact, both liberals and conservatives in most Western societies would be termed liberals, and some conservatives do call themselves "classical liberals."
Early history: The Enlightenment
John Locke etc, French revolution
20th century challenges
Fascism and communism
Liberalism's short-lived triumph
End of history, but then rise of Trump.
Tolerance of intolerance
Can liberalism tolerate anything other than itself
Deneen and why liberalism failed