The military advantage that the Qin had over the other northern states in battle was:
- Iron weapons
Iron weapons provided the Qin with a significant edge in warfare due to their strength, durability, and effectiveness in combat. These weapons, such as swords, spears, and arrowheads made of iron, were superior to the weapons used by other states that were made of bronze or other materials. The use of iron weapons allowed the Qin to have better offensive and defensive capabilities on the battlefield, giving them a strategic advantage over their adversaries.
In contrast, the other options listed in the question:
- Horse-drawn chariots
- Body armor
- An extensive navy
While these elements could provide certain advantages in specific situations, they did not offer the same level of overall military superiority as iron weapons did for the Qin during that time period.
