Complex sentence: Thus, the Sino-Soviet Treaty guaranteed Outer Mongolia's independence, but it also ended Khorloogiin Choibalsan's hopes for uniting Outer Mongolia with Inner Mongolia, which remained in China's hands.
Split into simpler sentences: Thus, the Sino-Soviet Treaty guaranteed Outer Mongolia's independence. But it also ended Khorloogiin Choibalsan's hopes for uniting Outer Mongolia with Inner Mongolia, which remained in China's hands.