Complex sentence: Fifthly, he led the campaign against Russia and helped Qing China reach a border treaty with Russia, because he had met the Russian regent Sophia Alekseyevna (蘇菲亞) earlier and helped her seize control over Russia.
Split into simpler sentences: Fifthly, he led the campaign against Russia and helped Qing China reach a border treaty with Russia. He had met the Russian regent Sophia Alekseyevna (蘇菲亞) earlier and helped her seize control over Russia.