Mysore was allied to the United Kingdom after the First Anglo-Mysore war around 1770. As such, they declared war as an ally of the UK, although they didn't contribute much, given the fact that they were on the other side of the world from the US.

Interestingly, though, Mysore would have an impact on the United States in the War of 1812. Mysorean rockets were simple crude rockets that were used by great effect by the Mysoreans against the British on several occasions. The British captured some of these rockets and redesigned them with the latest technology at the time, resulting in the Congreve rocket, a dumb-firing rocket that was used to great effect in the Napoleonic Wars and the War of 1812. In fact, in the US anthem, the line "the rockets' red glare" refers to the Congreve rockets deployed by the British in their assault on Fort McHenry!