a much stronger force was somehow vanquished by a small and poor African kingdom with a weak military.

Actually, you may have gotten things the other way around - a 18,000-men-strong expeditionary force under the command of the arguably incompetent Oreste Baratieri (Baratter) got lost, scattered and was subsequently ambushed during the night of the 1st of March, 1896, by some 40,000 Ethiopians armed with modern guns courtesy of France and Russia (who'd also sent military advisors). Think of Adwa as the very Italian equivalent to the Little Big Horn.

By the way... it was the First Italo-Abyssinian War.