India and Austrialia are relatively later ventures, but one person with an infamously firm grasp of just how small the British Isles were was American independence supporter Thomas Paine. His pamphlet, titled Common Sense, was arguably the piece of literature which sparked revolutionary fervor in the Thirteen Colonies. I could summarize his viewpoints, but Thomas Paine says it as well as I ever could.

...if they cannot conquer us, they cannot govern us. To be always running three or four thousand miles with a tale or a petition, waiting four or five months for an answer, which when obtained requires five or six more to explain it in, will in a few years be looked upon as folly and childishness—There was a time when it was proper, and there is a proper time for it to cease.

Small islands not capable of protecting themselves, are the proper objects for kingdoms to take under their care; but there is something very absurd, in supposing a continent to be perpetually governed by an island. In no instance hath nature made the satellite larger than its primary planet, and as England and America, with respect to each other, reverses the common order of nature, it is evident they belong to different systems: England to Europe, America to itself.

I don't know as much about the history of Canada/Australia/India/South Africa/any other particularly large British colony, but these themes of 'a continent perpetually governed by an island' - one of the most famous quotes in Paine's text - could easily be extrapolated onto any of those, especially India and Australia which are still sometimes considered continental landmasses in a way the U.S. never was.