Complex sentence: Russia gained control over a large part of Armenia become the protectorate of Armenians in the Ottoman Empire (a protectorate clause) and obtained the independence of Romania (see: National awakening of Romania) and Serbia.
Split into simpler sentences: Russia gained control over a large part of Armenia, and became the champion of Armenians in the Ottoman Empire (a protectorate clause). Russia was also instrumental in obtaining the independence of Romania (see: National awakening of Romania) and Serbia.