The last major nuclear weapons control treaty between the US and Russia, New START, expires this Thursday. Signed in 2010, the treaty capped deployed strategic nuclear warheads at 1,550 each and allowed inspections and data sharing. Its end marks a halt in arms control cooperation that helped ease Cold War tensions. Pope Leo urged both nations to renew the treaty, stating the world needs "doing everything possible to avert a new arms race." The original 1991 START treaty had limited warheads to 6,000. Despite a technical suspension three years ago, both countries had mostly followed the agreement. Other arms control agreements have already ended, including the Intermediate-Range Nuclear Forces Agreement, Open Skies Treaty, and Conventional Armed Forces in Europe Treaty. Admiral Sir Tony Radakin warned their collapse risks unraveling global security frameworks. Russia's Dmitry Medvedev called the treaty expiration alarming. US President Donald Trump seemed less worried, saying, "If it expires, it expires... We'll just do a better agreement." The US wants future treaties to include China, while Russia insists on including France and the UK. Experts highlight that both the US and Russia are modernizing nuclear arsenals and enhancing strategic weapons, fueling a new arms race. Russia is developing weapons like Poseidon, a nuclear-powered torpedo, and Burevestnik, a nuclear cruise missile. The US is working on the "Golden Dome" missile defense system. All three powers—US, Russia, and China—are advancing hypersonic missiles that fly faster than 4,000 mph and are harder to intercept. These developments make new arms control talks tougher. Darya Dolzikova of RUSI says more countries now seek nuclear deterrents, raising the stakes. Talks between Putin and Trump last year made no progress. With New START expired, the world faces a riskier and less predictable nuclear future.