Comment by Retric

The nice thing about maps is they show every country, so you can quickly see how few lack such links. If like tables add up what percentage of countries aren’t tied in with at least one of their neighbors. It’s a short list, even NK is tied to China.

You may discount England but it’s got enough DC links to move a large fraction of demand.

Japan has two networks for historic reasons, but they can move well over 2% of each grid’s average demand to the other. It’s just significantly less efficient but that’s relatively minor vs the other disadvantages of a split 50hz vs 60hz national grid.