Complex sentence: Kharkiv was the first city in Ukraine to acknowledge Soviet power in December 1917 and it was the capital of the Ukrainian Soviet Socialist Republic until January 1934, when the capital was moved to Kiev.
Split into simpler sentences: Kharkiv was the first city in Ukraine to acknowledge Soviet power in December 1917 and later became the capital of the Ukrainian Soviet Socialist Republic. Kharkiv remained the capital of the Ukrainian SSR until January 1934, when it was moved to Kiev.