What is the policy that conquering and rule other lands?

Imperialism.The term 'imperialism' should not be confused with ‘colonialism’ as it often is. Edward Saidsuggested that imperialism involved “the practice, the theory and the attitudes of a dominating metropolitan centre ruling a distant territory’”. He goes on to say colonialism refers to the “implanting of settlements on a distant territory”. A great example would be the Open Door Policy in China in the early 1900s