After briefly establishing himself as Emperor of China from 1915 to 1916, the death of dictator Yuan Shikai resulted in a period of political turmoil in China known as the Warlord Era, the most recent where country fell apart (again).
Along with territories already disputed with surrounding powers, China would lose effective control over Outer Mongolia until briefly reestablishing control from 1919 to 1921 and Tibet until 1951 after the fall of the Qing, rendering both regions de facto independent.
No cities of either of these two regions make the list with Lhasa being the largest of Tibet at 35,000 and Niislel Khüree (Ulaanbaatar) in Mongolia at 38,000.
Along with territories already disputed with surrounding powers, China would lose effective control over Outer Mongolia until briefly reestablishing control from 1919 to 1921 and Tibet until 1951 after the fall of the Qing, rendering both regions de facto independent.
No cities of either of these two regions make the list with Lhasa being the largest of Tibet at 35,000 and Niislel Khüree (Ulaanbaatar) in Mongolia at 38,000.