[dragonwriter]

> Three hundred years ago the US was a British colony.

Strictly, parts of the modern US were separate British colonies (colonies of the Kingdom of Great Britain, not the UK, which is newer.)

> Canada was technically a UK colony until the 1980s

Largely, it should be noted, because the Canadian provinces couldn’t agree on a method for amending the Constitution domestically to replace British Parliamentary authority.

> Countries don't buy and sell other counties anymore

I mean, Trump wanted to buy Greenland, but generally overt sale of inhabited territory is somewhat passé. Less direct means of buyingn coubtries are still, at least, actively pursued, if not always successful.