Genghis Khan was born near the Onon River about 300 kilometers northeast of Ulaan Baator in Mongolia. In connection with a rebellion against a local chieftain, Genghis Khan unified a number of tribes. This unity resulted in a military force that was unmatched during medieval times.
Erik Hildinger explains Mongolian successes like this:
The Mongol rode a pony that was considerably smaller than the war charger of the Western armies. The Asiatic animal, however, had superb endurance and survived by grazing in the wild. Each Mongol soldier had two, three or even four ponies so that he could spell them on a march and save them from exhaustion. That practice allowed Mongol armies to travel 50 or even 60 miles in a day, several times the distance that a Western army of the period could travel. It also gave the Mongol the edge in speed on the battlefield.
A Mongol commander might be anywhere in his formation, directing his troops as he saw fit. In contrast, the leader of a European army often fought alongside his men in the thick of battle where he was easily identified, in danger and unable to respond to developments in the fight. Such leadership by example made a certain amount of sense where battles were seen as opportunities for the display of personal bravery, where the object of the contest was honor as well as victory. But to the Mongols, victory was all that mattered. Consequently, their approach was to kill or defeat the enemy as efficiently as possible - that is, with the least cost to themselves. That was a logical approach for the Mongols, who campaigned thousands of miles from home against opponents who outnumbered them; they could not afford to lose either men or battles. Mongol tactics resembled those of the hunter, who uses speed, finesse and deception to herd his prey where he will, then kill it with as little risk to himself as possible."
In 1215 Genghis Khan led an attack on the Chinese city of Beijing. Although the city was defended by 600,000 men protected by 43 kilometers of fortifications, they were conquered by the 75,000 men of the Mongol army. Thereafter he directed his interests towards the west.
During the period of 1221-1223, Genghis Khan sent two of his generals along with an army of about 20,000 men on a reconnaissance mission across Ukraine, down through Turkey and Persia, up through Caucasus, through the Carpathians and back into Ukraine. Although this excursion led the Mongols far into the west, a major pocket of anti-Mongolian resistance remained in the southern Ukraine in the area of the Volga and Ural rivers near the coast of the Caspian Sea. Here, a chieftain named Bachman led forces composed both of local tribes and eastern refugees from earlier Mongolian attacks. After the death of Genghis Khan in 1227 his son Ogodei was chosen by clan leaders to become the new leader and sometime about 1235 Ogodei was able to defeat Bachman. With the consolidation of southern Ukraine under Mongolian rule the towns of Karakorum, Sarai Batu near Astrakhan on the lower Volga and Sarai Berke on the Volga near present-day Volgograd begin to serve as power centers of the growing Mongolian empire.
It was from these areas that Batu Khan, a grandson of Genghis Khan, launched invasions into Kiev and beyond in 1237. Over the next three years the Mongols destroyed all of the major cities of Ukraine and Russian with the exceptions of Novgorod and Pskov. Kiev was totally destroyed in 1240. The Mongol riders also made several attacks deep into Europe, into Hungry and Poland, returning to Ukraine in 1242. It has been suggested that the Mongolian style of warfare made it impossible for them to maintain more than a temporary presence in the more heavily forested areas of Europe. A Mongolian army of 20,000 men required 50 to 80 thousand horses and permanent upkeep of such a large number of animals on the more sparse pasturage of forested Europe was a difficult logistic problem. Like locusts, such a flock would have to be continuously on the move towards untouched greenery and the as yet unplundered haystacks of local peasants. This problem was less acute on the grassy steppes of central asia. The Mongols maintained a presence in Ukraine for 200 years.
Five years after the fall of Kiev, Papal envoy Giovanni di Plano Carpini wrote:
As a result of the destruction of the cities and the tribute demanded by the Mongols, the lack of resources brought Ukraine to a standstill. With the Mongols most strongly situated in the Ukrainian southwest, the northeastern Russian cities gradually gained more influence - first Tver, and then, around the turn of the 14th century, Moscow. It wasn't until 1480 that Moscow became strong enough to finally throw off Mongolian rule - the Mongols contributed to the ascendency of Moscow over Kiev.
Angus McBride's painting shown above depicts Mongol heavy cavalrymen in conflict with Teutonic knights outside the Polish city of Liegnitz in 1241 during the second incursion of Mongolian forces in Europe.