If the Indian rubber supply was destroyed or cut off due to border conflicts, and the Romans went on to discover Non-Newtonian synthetic silicone polymers, how would it have changed the face of warfare and the sweep of history since the time of Caesar?
Note that we were walking on the moon only 25 years after polydimethylsiloxane was discovered.
Edit: It's not "too broad" since I limited the scope to just warfare! Honest, that's the established precedent!