Why did john hay issue the open door policy?

The Open Door notes from John Hay were issued in 1899 to keep European powers from dividing up The Congo Basin and China. The US had become a Far Eastern power after acquiring The Philippine Islands following the Spanish-American war. It said that Africa (the Congo) and China were not to be partitioned by European powers. The unanimous acceptance of Hay's proposal made the Open Door an international policy. After WWII China became a completely sovereign state, and no nation had any right to carve out spheres of influence and the Open Door policy ceased to exist.