Complex sentence: China's unequal treaties almost completely dissolved only following Hong Kong's handover in 1997 (though it was agreed on in 1984 following talks between Deng Xiaoping and the British) with the exception of territory seized by Imperial Russia (Outer Manchuria) in 1860.
Split into simpler sentences: China's unequal treaties almost completely dissolved only following Hong Kong's 1997 handover. Exception of territory seized were made by Imperial Russia (Outer Manchuria) in 1860.