At around the year 1000AD, a trader from China travelled up the silk road, carrying with him, gunpowder. He reached the Byzantine Empire, and traded the gunpowder in Constantinople.
The Byzantine Empire had lost much of its land to Arabs, and with their new weapons, they seized the opportunity to take back their stolen lands and create a new Roman Empire.
The Byzantine's beat the Seljuk Turks out of Asia Minor by 1070, completely preventing the loss of Constantinople in 1453.
With the Mongol invasion of Russia, a fellow Orthodox country, in 1223 was halted by the Byzantines, who went on to take much of the Baltic for their own empire.
The Byzantine's gave the knowledge of gunpowder to their Russian allies, and they formed a powerful alliance, bringing much of Europe under their rule.
But the Mongols acquired gunpowder from the Chinese, but, because of their fear for the Byzantine-Rus alliance, they concentrated on taking over Asia, rather than Europe.
In 1492, Christopher Columbus sailed west in search of alternatives to trade routes blocked by the Byzantines, discovering the Americas. The Byzantines followed suite, and became a colonial power, well into the 1700's.