The history of this type of thing goes back even farther, to the mid-19th century -- see https://en.wikipedia.org/wiki/Filibuster_%28military%29.

(Back then it was Caribbean and Latin American states that were the usual targets, rather than African ones. But the same logic applies -- the targets were still relatively new post-colonial states, it's just that the colonial power that had most recently been losing its grip was Spain.)