It is first of all the belief that individual human beings are what matter most ― more than the state, or the total of national wealth, or anything else whatever.
It は前の文の democracy をさす
that は、同格の that = thatの直前のフレーズが名詞（句）で、that節が完全文（complete sentence）である
= something very recent
= the belief
= individual human beings are what matter most