US Flag Day (adopted 1777)… this looks a lot of fun:
Liberation Day (Falklands, South Georgia and South Sandwich Islands, from Argentina, 1982)
The Falklands may have originally been occupied by Patagonians but apparently when Europeans arrived it was deserted. English Captain John Strong was the first European to discover it in 1690. The French built Port Louis there in 1764, and the Brits built Port Egmont two years later, perhaps without knowing about each other.
Spain took the Falklands from France in 1766 then discovered the British port and, to avoid war, handed it to the Brits in 1771. British and Spanish settlements then co-existed on the island. Three years later the Brits left, but left a plaque saying it still belonged to them.The Spanish side became mainly a prison camp.
Then Buenos Aires (Argentina’s capital) claimed it, but in 1832 the Brits came back to kick them out. The Brits left again after, but as this caused more tension, they came back later to settle the island. It became an important point to reach the Antarctic.
It has been occupied by the Spanish, French and Argentinians, but Britain claimed it in 1833. There are fewer than 3,000 native Falklanders living there, most of whom had British ancestors, and are British citizens.