> Similarly with colonialism - that's something that is only possible once your society is already rich and powerful enough to go around and dominate others.

I disagree. The European colonial period started in the 15th Century[1]. It established the wealth and power of those nations for almost half a millennium following. The main enabler was not power and wealth, but technology (sailing ships)

> Colonialism was not a huge success for England when you look at how much it cost. It was great for national pride and as a symbol of their "greatness" however.

Again, I'm not sure is correct. By 1914, European colonial powers controlled 84% of the globe[1]. Effectively the only competition was other colonial powers and colonialism demonstrated itself as effective to achieve economic power through (ruthless) acquisition and exploitation of global resources.

[1] https://en.wikipedia.org/wiki/Colonialism