How a natural Strait of Panama rewrites global history

In a world with a natural Strait of Panama, who would fortify it and how important would it become?

Spain would probably fortify it first, and the passage would transform colonization, trade, and naval strategy across both American coasts.

The panel expects Spain to fortify a natural Strait of Panama first because Spanish power reached the region before later European rivals. Scotland's historical Darien ambitions show why other states would also contest a passage offering direct movement between oceans. The discussion then pushes the geography backward, asking whether Norse voyagers could pass through and reach the Pacific. By eliminating the overland barrier, the strait changes colonial routes, naval basing, commerce, and the strategic relationship between North and South America from the beginning of sustained European contact.