At the end of the Sino-Japanese War and Britain's refusal to join the Triple Intervention leads to Nicky and Willie going beserk. They decide to humiliate Britain for its treachery by rubbing Japan's nose in the dirt (Willie is convinced that Britain double crossed everyone and made a secret deal with Japan in OTL so this isn't all that radical. Willie always wanted to go further than Nicky)
To be polite, they invite Spain, who didn't like the Japanese in Taiwan, in on the fun- everyone takes it out on Japan stripping her of all her war gains. Russia gets Korea, Germany Taiwan, France Okinawa and Spain gets the Japanese fleet (including all the ships that Japan is building) and everyone splits the indemnity.
This would give the Spanish a sizable addition to her fleet (two first class battleships, a bunch of torpedo boats and about ten cruisers) that would make a major contribution to the Spanish fleet
The torpedo boats would be the key as they could use them to make the landings in the Philippines and Cuba very costly. Meanwhile, the cruisers and battleships inflict major damage on America's trading routes. The war drags out raising the American death toll from disease and bringing the war fever to an end. Finally, the Americans accept Papal mediation on the basis of status quo ante bellum to get out of the jam when Germany, Russia and France offer armed mediation (at McKinley's request). Russia will only intervene if the Americans ask for it, Germany, Italy and Austria probably would have if they were convinced of English neutrality. France might have but (the Kaiser thought there was hope) but Russia would have none of it