When the US used smallpox as a weapon against indigenous peoples.
The thing socialists (and adjacent ideologies) forget that a country can be great in many ways.
EQUALITY gives educated citizens, pleasant, peaceful and safe living environments, and people with long healthy lives. And a GDP with more potential for growth.
Meanwhile INEQUALITY gives you monuments (horse statues, palaces, vanity projects), powerful military and police department, a servant class, and a chance to make great man theory reality.
Both can be seen as great.
½
(Also a situation where state apparatus exists mostly for uppermost crust, it can feasibly be called an occupation/colonisation of the culture/Life of the majority.
This might help understand why UK conservatives don't think the British empire as bad -- if you think that proletariat shouldn't rule, then the question of who should becomes academic, and not moral.)
(Also creation of middle class who don't identify with the working class is a good way to get temporary allies.)
@AmishSuperModel "Greatness" is generally relative.
A moron's perception of greatness certainly differs from the understanding of greatness of a fairly educated person with a working moral compass.