What was the Open-Door Policy, and how did the Boxer Rebellion illustrate its value?

Open-Door Policy definition and the way how the Boxer Rebellion illustrated its value are as follows:

Open door policy is the policy adopted by the United States of America between 1899 and 1900. According to this policy, countries were to get equal access to the ports of China for trade.

This policy was approved by a lot of countries around the world and it is regarded as one of the most important foreign policies of America with South East Asia. Due to the boxer Rebellion a lot of global powers did not agree with the ideologies.