The application of this principle has proven to be the single most divisive political issue between Parties over the life of the Convention. Unlike the UNFCCC, the Kyoto Protocol contained quantifiable binding emission reduction targets for industrialized countries in Annex I.70 This represented the application of the principle of common but differentiated responsibilities at that time. The Protocol finally entered into force on 16 February 2005. In spite of its entry into force, however, several major emitters remained outside mandatory emissions regime, either because they were non-Annex 1 countries, such as China and India, or because they were unwilling to sign on to the Protocol, such as the United States of America.