"principles that made them great..."
What principles would that be? I see a statue of Lincoln in the video so are we to assume that fighting a cινιℓ ωαr over tariffs and other ideological issues is "great"? Are we to assume that writing a Declaration of Independence about equality, which Jefferson did not really believe by the way, is great?
Also if we look at the video we are to assume that democratic capitalism is the only way to build a successful society which simply is not true as societies more often than not are built on authoritarianism and repression. In fact China itself shown in the video is built on the economic model of Freidrich List, of repression, autocracy, authority, mercantilism, etc. while America is on the decline because of democratic capitalism.
Societies do not necessarily decline because of economic models. Societies do decline however because of the sickness of their moral issues.