The Mongol threat reaches Europe. In 1241, two Mongol armies invaded Eastern Europe. At Liegnitz, an army of German and Polish knights was defeated by one, while the main Hungarian army was cut apart by the second at the Battle of the Sajo River. Internal divisions within the Mongol Empire saved Western Europe from invasion in the following years.

A mixed Slavic army led by the Serbs is crushed by the Ottoman Turks under Sultan Murad I, in 1389 at the Battle of Kosovo, although Murad himself is killed. The Emir (prince) Osman, who lived around 1300, and his son, had founded the Ottoman dynasty, by breaking free from Mongol rule. Ottoman comes from the Arabic form of his name, "Othman".

Constantinople itself was taken by the Ottoman Turks under Sultan Mehmed in 1453. The siege began on April 6. The world's largest cannon, one with a barrel eight metres long, hurled huge stone balls at the triple walls surrounding the city. In an amazing feat, a fleet of small Turkish ships was hauled overland in one night and moved into the main harbor, which the defenders had thought safe because it had been closed off with a huge chain. But it was the land assault of May 29, that finally broke through the city's walls. At the end of a day of pillage, Mehmed, now called "the Conqueror", entered Constantinople to restore order and to pray in the Church of Hagia Sofia, now at his order turned into a mosque. In addition to his other titles, Mehmed now called himself the Roman emperor, or "Rum Kayseri". The Ottoman sultanate was now an empire.

Hildegard (born 1099, died 1179), a German nun, becomes equally famous for her mystical visions, and her music and poetry. She was also a prolific writer, producing books on natural history, medicine and the lives of saints. Hildegard eventually becomes the abbess of the nunnery at Bingen on the Rhine River.

Even at the peak of the viking raids, Frisian merchants had been the most important traders of Europe, with trade routes reaching from the Rhine delta area into Russia and the Mediterranean. The Frisians were a collection of loosely united merchant towns dotting the North Sea coast of the Netherlands and Germany. By 1300, the Frisians were losing out to a new commercial rival, the Hanseatic League. The League was a union of a dozen Dutch and German ports, the most important of which was Hamburg.

Around 1140, a Frisian ship attempted to reach the North Pole in perhaps the first voyage of its kind. The ship got stuck in ice near Greenland, but managed to escape and return home. The typical medieval ship of Europe, the round-hulled cog, was in wide use by 1300. The Frisians had used a smaller type of this ship by at least 800 AD. Unlike the viking dragon ship, which was long and relatively narrow (thus making it very fast), the new Frisian cogs, which appeared around the year 1000, were larger and wider, with higher and steeper hulls (the sides of a ship are called gunwales). They were heavier and slower than the longship, but could carry more cargo and were sturdier. Before the invention of cannon, the ship with the higher gunwales had the advantage in battle because you could jump down onto an enemy ship instead of having to climb up, and the new cogs were part of the reason for the decline of the vikings. One large cog was considered worth ten longships. The cog was even strong enough that small wooden towers, called castles, could be built at each end of the ship (the name for the front part of a ship is still "forecastle"). Although great mariners, even the vikings usually stuck close to shore. The cog allowed Europeans to sail far out into the ocean. Led by the Portuguese, the worldwide expansion of the Europeans was about to begin.