Gunpowder is a composition of sulfur, charcoal, and saltpeter that becomes a highly flammable and explosive powder. It was first invented in China, and was fashioned into incendiary weapons and prototype cannons. An example would be the Chinese fire arrow, which were essentially primitive rockets. The secrets of gunpowder would be mostly monopolized by China until around the 13th century, when technologies were traded along the Silk Road.
Illustration of early Chinese gunpowder weapon.
While previous military advancements such and iron working and cavalry enhanced the potency of foot soldiers, gunpowder completely renovated defensive and siege warfare. Previous examples of revolutionary siege technologies included catapults and trebuchets, both aimed towards launching projectiles over castle walls. However these large contraptions were prone to misfiring and were generally quite clunky to use. Cannons became the siege weapon of choice once gunpowder became a widespread technology, as they were more compact and consistently powerful. In addition to the effectiveness of these new weapons, they also had a powerful psychological impact on early battles fought against clueless enemies. This resulted in convincing early victories, for example, it allowed China to repel Mongol invaders (until the Mongols began to grow accustomed and develop gunpowder weapons of their own).
The Korean Hwatcha, a contraption that bombarded an area with small rockets.
From a political standpoint, the innovation of gunpowder gave rise to several "gunpowder empires", who used this new military technology to make a name for themselves by force. These included the Ottoman Empire, the Safavid Empire, and the Mughal Empire. The Ottomans would go on to utilize gunpowder technology with their Janissaries to conquer Constantinople and most of the land around the Mediterranean. This allowed them to force themselves into a position of worldwide power.