If you're asking about a power that wholesale defeated/conquered the united Mongol Empire, then the answer is no outside power. The disintegration of the united Mongol Empire was done internally through a series of succession disputes as well as little in the way of infrastructure to effectively govern such an immense stretch of territory in any centralized manner, leading to the division of Mongol territories into various successor states that were eventually conquered or collapsed in the following centuries.

Möngke Khan, who ruled the united Mongol Empire until 1259 died without a clear heir, sparking the Toluid Civil War between Kublei Khan and Ariq Böke, both grandsons to Genghis Khan for the title of Khagan (Great Khan). Kublei Khan won the civil war in 1264, but his position of Khagan was mostly a nominal title due to mounting difficulties in governing such vast stretches of land from Korea to the borders of Poland and the Byzantine Empire. Kublei Khan's direct control was mostly centered around China, where he was declared the first Emperor of the Yuan Dynasty, while other, more distant descendants of Genghis Khan began to assume control of the periphery territories.

With the death of Möngke Khan, the empire was effectively divided into 4 major successor states during the Civil War and Kublei Khan's reign. The Yuan Dynasty, and the de jure Khagans of the Mongol Empire under Kublei Khan retained control of China and present day Mongolia proper. The territories of the northwest became the Golden Horde in control of modern day Russia and Kazakhstan. Territories in Persia/the Middle East became the Ilkhanate, and the remaining territories in Central Asia around Kyrgyzstan and Afghanistan became the Chagatai Khanate. Here's a map for better visual.

These successor states however were eventually conquered throughout the centuries. The Golden Horde gradually lost control of its tributaries in Russia due to the growing power of Moscow and would slowly be conquered by Russia, with their last holdout being the Khanate of Crimea which was annexed by Catherine the Great in 1783.

The Ilkhanate didn't last near as long, the arrival of the Black Plague devastated the Khanate in 1335 and was fractured into various of Persian successor states, the most prominent of them being the Muzaffarids, but later they and all the other successor states were conquered by the rising Timurid Empire in the 1380's-90's. The Chagatai Khanate, the birthplace of Timur, was conquered by him in the 1370's.

The Yuan Dynasty, and the most direct line of Mongol succession was overthrown by the Hongwu Emperor in 1368 following the Red Turban Rebellion, founding the Ming Dynasty of China after the disintegration of Yuan control. The Yuan Dynasty retreated north and remained in present day Mongolia, fighting with rival hordes such as the Oirats until Hong Taiji, the first Emperor of the Qing Dynasty invaded Mongolia, conquering the last remnants of the Yuan in 1635.

Sources:

The Mongol Empire and Its Legacy by Reuven Amitai, David Orrin Morgan

A Concise History of the Rise and Fall of the Mongolian Empire by Henry Harrison Epps

The Empire of the Steppes: A History of Central Asia by René Grousset