What was a precursor event that ended up being a dry-run for a subsequent conflict in history?

This is a concept often discussed in the context of World War 1 and World War 2, with several conflicts having been dry-runs for those two large-scale wars. The Italo-Turkish War, the Balkan Wars and the Chaco War are all examples of smaller conflicts that served as a testing ground for tactics, strategies and weapons that would later see use in World War 2. In the case of World War 1 however, it was often the case that techniques that were used in the Crimean War, the Austro-Prussian War, the Franco-Prussian War and others were later put into action during the Great War.<br><br>Examples of such conflicts that served as a precursor event for a subsequent war can be found all throughout history. In the case of the United States, The Iraq War saw NM257 and the sticky-bomb IEDs that were used against the British in Iraq in the 1920s see a return in Iraq in the 2000s and 2010s, as part of an anti-occupation insurgency. That same insurgency also saw the return of the booby-trapped corpses that were used by the Germans in the 1940s.