Pirates win: Why? I get British Empire ticked off at Japan over some tea poisoning. Japan sends ninjas to kill King George the Third, and due to British Uber-awesomeness, all the ninjas die and are drawn and quartered. This makes the Austrian and Prussian Kings very happy, and they join in an alliance. The British nationalism triggered prevents the revolution from and keeps Britain's industry at top speed. The British Parliament annexes the West Indies (Pirate Capital) and causes them to become a protectorate of the British Empire. France and Spain bickering again causes the Anglo-German-Pirate alliance to gain territory, France surrenders, and Austria captures Spain and makes Carlos feel like an idiot again. Russia like and joins in after beating the Sweds in the arse because Britain forgot about them... again. The Ottoman Empire than joins in, for no reason whatsoever except that otherwise... ouch. The truce with the Japanese ends when they attack... again. This event kills the Russian Czar in the assassination wave, as well as the Pirate Lord. The Anglo-German-Spain-Austrian-Russian-Pirate-America-Canadian Alliance than launches a full scale attack on Japan (we will give them, China to make it fair xD)
ON the Land: Villages are bombed with cannons and bombards and rocketry, while line infantry divisions eat up poor ninjas. Puckle guns force horse riding ninjas and mass waves of ninjas to--- rethink their attack. The new invention--- quicklime... causes Tree-Borne ninjas to---- burn up?
On the sea: The very small Sampans are wiped out by a wave of steamships and Ludicrously Large Line of Battleships. Don't ask me how bad this ends.
So, in the end, the ninjas are wiped out, and by British custom, they are put in the Tower of London (and its copy, built right after the space shortage) and all put on the rack! The Japanese Empire splits into two, and suffers a revolution and under the strain of the Western might, Capitulates.
Bah, curses are no bother to pirates. Pirates get cursed all the time. Unless its Davy Jones coming to collect their soul, they could care less. They'll just make a deal somewhere to break the curse and fight another day.
I don't like ninjas, but I'm afraid to say they have more combat skill. Pirates have brute force but ninjas have speed and can use more than just a sword for a weapon. I think ninjas would win. However I still like pirates more.