Imperialism and expansionism is often rooted in the idea that the peoples of different countries and their respective governments have different merit or value, and one should rule over the other.
Once you start talking about hierarchies among nations and ethnicities, you are starting to establish connections with other concepts that relate to one type of people being exceptional and entitled to rule over others: nationalism and racism.
Imperialism, nationalism and racism are deeply interconnected: if all peoples had similar value or merit there should be no need to change borders because what's outside your borders is similar to what's inside your borders.
The way imperialists talk by highlighting how exceptional your nation and people are or can be, and contrasting against other nations and peoples. And how expanding and ruling others would further improve things.
