Why is China in the UN?

Here is the a piece of the Charter of the United Nations:
WE THE PEOPLES OF THE UNITED NATIONS DETERMINED

• to save succeeding generations from the scourge of war, which twice in our lifetime has brought untold sorrow to mankind, and
• to reaffirm faith in fundamental human rights, in the dignity and worth of the human person, in the equal rights of men and women and of nations large and small, and
• to establish conditions under which justice and respect for the obligations arising from treaties and other sources of international law can be maintained, and
• to promote social progress and better standards of life in larger freedom

Tibet?