The United States’ ability to influence events in the Mideast has waned, and other major nations have essentially been onlookers.Over almost a year of war in the Middle East, major powers have proved incapable of stopping or even significantly influencing the fighting, a failure that reflects a turbulent world of decentralized authority that seems likely to endure.Stop-and-start negotiations between Israel and Hamas to end the fighting in Gaza, pushed by the United States, have repeatedly been described by the Biden administration as on the verge of a breakthrough, only to fail. The current Western-led attempt to avert a full-scale Israeli-Hezbollah war in Lebanon amounts to a scramble to avert disaster. Its chances of success seem deeply uncertain after the Israeli killing of Hassan Nasrallah, the longtime leader of Hezbollah on Friday.“There’s more capability in more hands in a world where centrifugal forces are far stronger than centralizing ones,” said Richard Haass, the president emeritus of the Council on Foreign Relations. “The Middle East is the primary case study of this dangerous fragmentation.”The killing of Mr. Nasrallah, the leader of Hezbollah over more than three decades and the man who built the Shiite organization into one of the most powerful nonstate armed forces in the world, leaves a vacuum that Hezbollah will most likely take a long time to fill. It is a major blow to Iran, the chief backer of Hezbollah, that may even destabilize the Islamic Republic. Whether full-scale war will come to Lebanon remains unclear.“Nasrallah represented everything for Hezbollah, and Hezbollah was the advance arm of Iran,” said Gilles Kepel, a leading French expert on the Middle East and the author of a book on the world’s upheaval since Oct. 7. “Now the Islamic Republic is weakened, perhaps mortally, and one wonders who can even give an order for Hezbollah today.”For many years, the United States was the only country that could bring constructive pressure to bear on both Israel and Arab states. It engineered the 1978 Camp David Accords that brought peace between Israel and Egypt, and the Israel-Jordan peace of 1994. Just over three decades ago, Prime Minister Yitzhak Rabin of Israel and Yasir Arafat, the chairman of the Palestine Liberation Organization, shook hands on the White House lawn in the name of peace, only for the fragile hope of that embrace to erode steadily.We are having trouble retrieving the article content.Please enable JavaScript in your browser settings.Thank you for your patience while we verify access. If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.Thank you for your patience while we verify access.Already a subscriber? Log in.Want all of The Times? Subscribe. More