Complex sentence: The first official mention of the term was at the 19th National Congress of the Communist Party of China and it has gradually been developed since 2012 after Xi became General Secretary of the Communist Party (China's paramount leader).
Split into simpler sentences: The first official mention of the term was at the 19th National Congress of the Communist Party of China. It has gradually been developed since 2012, after Xi became General Secretary of the Communist Party (China's paramount leader).