Original: During the collapse of the Qing Dynasty in 1911, Mongolia declared independence, but had to struggle until 1921 to firmly establish de-facto independence, and until 1945 to gain international recognition.
Simplified: During the collapse of the Qing Dynasty in 1911, Mongolia declared independence, but had to struggle with the Soviet Union's help, until 1921 before the world exsepted it's indpendence.