Answer based on context:

On 10 March 1912, Yuan Shikai was sworn as the second Provisional President of the Republic of China in Beijing. The government based in Beijing, called the Beiyang Government, was not internationally recognized as the legitimate government of the Republic of China until 1928, so the period from 1912 until 1928 was known simply as the "Beiyang Period". The first National Assembly election took place according to the Provisional Constitution. While in Beijing, the Kuomintang was formed on 25 August 1912. The KMT held the majority of seats after the election. Song Jiaoren was elected as premier. However, Song was assassinated in Shanghai on 20 March 1913, under the secret order of Yuan Shikai.

How many years after Yuan Shikai was sworn as the second Provisional President of the Republic of China in Beijing was it before the government was seen as a legitimate government internationally?
16