In The Possessed, Dostoyevsky has his character Shatov exclaim:

If a great people does not believe that the truth is only to be found in itself alone (in itself alone and exclusively); if it does not believe that it alone is fit and destined to raise up and save all the rest by its truth, it would at once sink into being ethnographical material, and not a great people…

Put another way, if a nation has confidence in itself, it continues as a viable political entity. Once it loses that, it lacks cohesion and becomes only a collection of random people living together.

In the 19th century, the British people believed in themselves. This confidence fueled their impetus for Empire; they embraced the need, the duty, even, to bring democracy, Christianity, and the British way of life to the entire world. No one doubted their heaven-sent mandate to do so. So much so, that Britain almost singlehandedly assumed the mission of ending the slave trade. As much as one-sixth of the Royal Navy was eventually assigned to this task, patrolling the Atlantic, and eventually freeing in the process 150,000 African captives. 

In Zanzibar, the ancient Muslim slave market was closed and an Anglican church erected on the spot, with the slave whipping post being exchanged for an altar. Truth, justice, and righteousness had prevailed, thanks to British arms.

In another part of Africa, David Livingston, after observing an Arab slave raid on an African village, devoted himself to the crusade -- there is no better term for it -- against the traffic, becoming an English hero for so doing.

And if my disclosures regarding the terrible Ujijian slavery should lead to the suppression of the East Coast slave trade, I shall regard that as a greater matter by far than the discovery of all the Nile sources together. -- (Livingstone in a letter to the editor of the New York Herald)

In India, the thug cult of stranglers was suppressed. As was Sati, by General Charles Napier:

This burning of widows is your custom; prepare the funeral pile. But my nation has also a custom. When men burn women alive we hang them, and confiscate all their property. My carpenters shall therefore erect gibbets on which to hang all concerned when the widow is consumed. Let us all act according to national customs."  

Fast forward now to the America of the 21st century. A U.S. Army soldier hears the screaming of young boys as they are being sexually abused by Afghan police. "At night we can hear them screaming, but we're not allowed to do anything about it." His superior officers, according to the account, "told him to look the other way because it's their culture." 

It is not an American custom. But America no longer believes that it has any right to intervene. All cultures are alike, we have been told; no one is better than any other, not even our own. We have lost our moral confidence.

If you want to destroy a nation, you find a way to denigrate its belief in itself. Smear its founders. Belittle its accomplishments. Pillory it for failing to live up to its ideals. Mock its most sacred traditions. Deride its heroes.

In the end, you will no longer have a nation, but only a collection of tribes, who occupy the same space but share no common concepts. There is nothing to unify them. In other words, you will be able to pinpoint that country with geographical data, but you will not find a national people.

One can argue that Britain ceased to be a nation when "to be British" no longer referred to a shared set of cultural beliefs. Today we may speak only of the "British Isles". America too now has headed down that long path to cultural oblivion. Being "American" once meant mom, apple pie, Sunday School, fair play, democracy, equality, and decency. But who is there going to be left who retains the moral confidence necessary to be an American in that old sense, once our political and academic leaders have finished their job of wrecking our past?