25 Days to Aden is the story of how in a week in 2015 the Gulf States pulled together a ten-nation coalition and the biggest military operation they ever launched unilaterally. It is an amazing account of Arab militaries doing what America would not, preventing Iran from taking a foothold on the Arabian Peninsula. The risks for global security were huge: Iran already overshadowed one of the world's greatest maritime straits, at Hormuz, and now it sought to dominate the southern approaches to the Suez Canal as well. Aden had to hold out against the Houthis. The Gulf States were used to America stepping up at such moments, but the White House was partway through negotiating a nuclear deal with Iran. No help would come from Washington. Instead, for the first time, the Gulf States acted alone. Told by an expert communicator on the region, it is a unique story. If the US is truly a global empire in decline, then the story may hold important pointers for a future of warfare driven by emergent powers in the gap left by the withdrawal of American influence.