A new treaty agreed to in the early hours of Friday by 23 European Union countries, including all 17 euro zone states, may be the most direct discussion of what constitutes sovereignty since the creation of the United Nations. The intergovernmental pact is a major step toward closer integration for the 17 countries that use the euro as currency, as well as the six that hope to join in the future. British Prime Minister David Cameron vetoed a plan by France and Germany to make changes to the EU treaties that would affect all 27 EU nations, saying the deal was not in the U.K.’s interests. Steven Erlanger, Paris bureau chief of The New York Times, reports on the latest from the EU summit in Brussels. Jonathan Tepper, chief editor at Variant Perception, an economics research firm, discusses the impact of the treaty, and Britain’s reasons for not participating.