Why Does China Think It Owns Taiwan?

Who said that China WANT TO own Taiwan? In fact,China don't want Taiwan at all. But why do China THINK Taiwan belong to them? It's easy.If China recognizes Taiwan IS a country,Tibet will said that since Taiwan is a country,Tibet can be a country,too. To avoid this event happen, China never recognize Taiwan owns its government. Once the politician of China said that China don't want Taiwan at all,if it was not Tibet,China will let Taiwan be independent as soon as possible. The problem of Taiwan has persecuted China for a long time.