What innovation would later have the greatest impact on warfare? black powder calligraphy movable type examination system

Black powder was the innovation that would later have the greatest impact on warfare.

Black powder is the earliest known chemical explosive. It consists of a mixture of sulfur (S), charcoal (C), and potassium nitrate (saltpeter, KNO3). It was invented in 9th-century China and spread throughout most parts of Eurasia by the end of the 13th century.  

Gunpowder was employed to fill fused artillery shells until the second half of the 19th century.

a king decides to declare war on a neighboring country without the input of any advisers