I was always taught that the first European settlement in the U.S. was St. Augustine, Florida claimed by the Spanish (who were claiming everything in the New World at the time) in 1565. It turns out, though, that my teachers were wrong. Or perhaps just misinformed.
Fort Caroline was established by French Huguenots in 1564. It is north of what would become St. Augustine on the Atlantic coast of Florida south of Georgia. The man responsible was French Admiral Gaspard de Coligny who financed an expedition of Protestant exiles from France to settle in the Americas. This was not a settlement in the sense that Jamestown or New Orleans would be settlements. This was a fort built for one purpose only: to serve as a base from which to raid Spanish shipping. As de Coligny himself described it:
There were no tillers of the soil, only adventurous gentlemen, reckless soldiers, discontented tradesmen, all keen for novelty and heated by dreams of wealth.
What de Coligny doesn't mention is a visceral hatred of the Spanish. Like the Buccaneers of Tortuga a century later, the Frenchmen of Fort Caroline saw Spain as their mortal enemy.
From Fort Caroline, the freebooters went out and raided not only Spanish merchants and treasure ships but Spanish cities as well. Cartagena and Panama in South America both fell prey to the Protestant pirates. Cuba was hit particularly hard - probably due to proximity - with both Santiago and the well established capital of Havana sacked and plundered.
Of course the Spanish weren't going to hold still for all these Froggy shenanigans. In 1565 King Philip II sent a force led by Captain General Pedro de Menendez of Avilles to deal with the problem. 30 ships left Cadiz in June carrying a force of 2,000 soldiers along with upwards of 500 settlers. The Captain General was charged by the king to handle the pirate problem and establish a Spanish fort in "The Florida". De Menendez was the right man for the job not only because of his ruthlessness but his business interests as well. He owned several merchant ships, one of which had recently gone missing in the area of Fort Caroline with his own son aboard.
By September, de Menendez was reconnoitering Fort Caroline and he didn't like what he saw. The triangle shaped fort was heavily armed with earthworks and high walls on all three sides. It had a good view of it's harbor and sat slightly back on an estuary the could become a tap for the Spanish ships. De Menendez took his men and settlers south and, finding what he referred to as "a good harbor" he officially established St. Augustine.
While in the process of building his own ramparts, de Menendez and his men saw a flotilla of pirate ships from Fort Caroline sail by heading south. He surmised that the fort might be left with only a few men and he marched his soldiers overland to try and take it immediately. His hunch was right and the poorly defended fort was overcome with no Frenchmen left alive.
De Menendez left troops at Fort Caroline and returned to St. Augustine. There he was informed that the French ships previously seen had been wrecked on the coast further south. De Menendez hurried to the site and found 200 surviving pirates. He had them slaughtered on the beach. Shortly thereafter, de Menedez caught up with the last of the Fort Caroline freebooters. All were executed directly, including the commander of the fort, Jean de Ribault.
A mass grave was dug for these men and over it de Menendez erected a marker which read: "I do this not to Frenchmen but to heretics."
As a reward for his effective viciousness, the King made de Menendez Governor of Havana, among other things. The Spanish Main would remain relatively safe for another five years. Then El Dragon, Sir Francis Drake, would pick up where the Huguenots pirates left off.