which event proved that the US purchase of Alaska has been a good investment?

Alaska quickly became one of the most populous US states

The United States profited from the eventual discovery of gold in Alaska

Russia suffered an economic collapse after selling off its access to Alaskan resources

Great Britain offered to buy Alaska for more than the United States have paid for the territory

The event that proved that the US purchase of Alaska has been a good investment is when Russia suffered an economic collapse after selling off its access to Alaskan resources.