Negative Effects on Europe
The Mongol Empire's expansion into Europe had several negative effects, especially considering their violent and destructive habits of invasion. The Mongols wiped out the populations of some entire towns that resisted--as was their usual policy--depopulating some regions and confiscating the crops and livestock from others. This type of total warfare spread panic even among Europeans not directly affected by the Mongol onslaught and sent refugees fleeing westward.
Perhaps even more importantly, the Mongol conquest of Central Asia and Eastern Europe allowed a deadly disease--likely the bubonic plague--to travel from its home range in western China and Mongolia to Europe along newly restored trade routes.
In the 1300s, that disease--known as the Black Death--wiped out approximately one-third of Europe's population. The Bubonic plague was endemic to fleas that live on marmots in the steppes of eastern Central Asia, and the Mongol hordes inadvertently brought those fleas across the continent, unleashing the plague on Europe.
Positive Effects on Europe
Although the Mongol invasion of Europe sparked terror and disease, it also had some positive impacts. The foremost was what historians call the "Pax Mongolica" — a century of peace among neighboring peoples who were all under Mongol rule. This peace allowed for the reopening of the Silk Road trading routes between China and Europe, increasing cultural exchange and wealth all along the trade paths.
The Pax Mongolica also allowed monks, missionaries, traders, and explorers to travel along the trade routes. One famous example is the Venetian trader and explorer Marco Polo, who traveled to the court of Genghis Khan's grandson Kublai Khan at Xanadu in China.
The Golden Horde's occupation of Eastern Europe also unified Russia. Prior to the period of Mongol rule, the Russian people were organized into a series of small self-governing city-states, the most notable being Kiev.
In order to throw off the Mongol yoke, the Russian-speaking peoples of the region had to unite. In 1480, the Russians--led by the Grand Duchy of Moscow (Muscovy)--managed to defeat and expel the Mongols. Although Russia has been invaded several times by the likes of Napoleon Bonaparte and the German Nazis, it has never again been conquered
