structural:summarization
Statehood and Indian removal

Defense of Florida's northern border with the United States was minor during the second Spanish period. The region became a haven for escaped slaves and a base for Indian attacks against U.S. territories, and the U.S. pressed Spain for reform.

Americans of English and Scots Irish descent began moving into northern Florida from the backwoods of Georgia and South Carolina. Though technically not allowed by the Spanish authorities and the Floridan government, they were never able to effectively police the border region and the backwoods settlers from the United States would continue to immigrate into Florida unchecked. These migrants, mixing with the already present British settlers who had remained in Florida since the British period, would be the progenitors of the population known as Florida Crackers.

These American settlers established a permanent foothold in the area and ignored Spanish authorities. The British settlers who had remained also resented Spanish rule, leading to a rebellion in 1810 and the establishment for ninety days of the so-called Free and Independent Republic of West Florida on September 23. After meetings beginning in June, rebels overcame the garrison at Baton Rouge (now in Louisiana) and unfurled the flag of the new republic: a single white star on a blue field. This flag would later become known as the " Bonnie Blue Flag ".

In 1810, parts of West Florida were annexed by the proclamation of President James Madison, who claimed the region as part of the Louisiana Purchase. These parts were incorporated into the newly formed Territory of Orleans. The U.S. annexed the Mobile District of West Florida to the Mississippi Territory in 1812. Spain continued to dispute the area, though the United States gradually increased the area it occupied. In 1812, a group of settlers from Georgia, with de facto support from the U.S. federal government, attempted to overthrow the Floridan government in the province of East Florida. The settlers hoped to convince Floridians to join their cause and proclaim independence from Spain, but the settlers lost their tenuous support from the federal government and abandoned their cause by 1813.

Traditionally, historians argued that Seminoles based in East Florida began raiding Georgia settlements and offering havens for runaway slaves. The United States Army led increasingly frequent incursions into Spanish territory, including the 1817–1818 campaign against the Seminole Indians by Andrew Jackson that became known as the First Seminole War. The United States now effectively controlled East Florida. Control was necessary according to Secretary of State John Quincy Adams because Florida had become "a derelict open to the occupancy of every enemy, civilized or savage, of the United States, and serving no other earthly purpose than as a post of annoyance to them."

More recent historians describe that after U.S. independence, settlers in Georgia increased pressure on Seminole lands, and skirmishes near the border led to the First Seminole War (1816–19). The United States purchased Florida from Spain by the Adams-Onis Treaty (1819) and took possession in 1821. The Seminole were moved out of their rich farmland in northern Florida and confined to a large reservation in the interior of the Florida peninsula by the Treaty of Moultrie Creek (1823). Passage of the Indian Removal Act (1830) led to the Treaty of Payne's Landing (1832), which called for the relocation of all Seminole to Indian Territory (now Oklahoma). Some resisted, leading to the Second Seminole War, the bloodiest war against Native Americans in United States history. By 1842, most Seminoles and Black Seminoles, facing starvation, were removed to Indian Territory west of the Mississippi River. Perhaps fewer than 200 Seminoles remained in Florida after the Third Seminole War (1855–1858), having taken refuge in the Everglades, from where they never surrendered to the US. They fostered a resurgence in traditional customs and a culture of staunch independence.

Florida had become a burden to Spain, which could not afford to send settlers or troops due to the devastation caused by the Peninsular War. Madrid, therefore, decided to cede the territory to the United States through the Adams–Onís Treaty, which took effect in 1821. President James Monroe was authorized on March 3, 1821, to take possession of East Florida and West Florida for the United States and provide for initial governance. On behalf of the U.S. government, Andrew Jackson, whom Jacksonville is named after, served as a military commissioner with the powers of governor of the newly acquired territory for a brief period. On March 30, 1822, the U.S. Congress merged East Florida and part of West Florida into the Florida Territory.

By the early 1800s, Indian removal was a significant issue throughout the southeastern U.S. and also in Florida. In 1830, the U.S. Congress passed the Indian Removal Act and as settlement increased, pressure grew on the U.S. government to remove the Indians from Florida. Seminoles offered sanctuary to blacks, and these became known as the Black Seminoles, and clashes between whites and Indians grew with the influx of new settlers. In 1832, the Treaty of Payne's Landing promised to the Seminoles lands west of the Mississippi River if they agreed to leave Florida. Many Seminole left at this time.

Some Seminoles remained, and the U.S. Army arrived in Florida, leading to the Second Seminole War (1835–1842). Following the war, approximately 3,000 Seminole and 800 Black Seminole were removed to Indian Territory. A few hundred Seminole remained in Florida in the Everglades.

On March 3, 1845, only one day before the end of President John Tyler 's term in office, Florida became the 27th state, admitted as a slave state and no longer a sanctuary for runaway slaves. Initially its population grew slowly.

As European settlers continued to encroach on Seminole lands, the United States intervened to move the remaining Seminoles to the West. The Third Seminole War (1855–58) resulted in the forced removal of most of the remaining Seminoles, although hundreds of Seminole Indians remained in the Everglades.

The first settlements and towns in South Florida were founded much later than those in the northern part of the state. The first permanent European settlers arrived in the early 19th century. People came from the Bahamas to South Florida and the Keys to hunt for treasure from the ships that ran aground on the treacherous Great Florida Reef. Some accepted Spanish land offers along the Miami River. At about the same time, the Seminole Indians arrived, along with a group of runaway slaves. The area was affected by the Second Seminole War, during which Major William S. Harney led several raids against the Indians. Most non-Indian residents were soldiers stationed at Fort Dallas. It was the most devastating Indian war in American history, causing almost a total loss of population in Miami.

After the Second Seminole War ended in 1842, William English re-established a plantation started by his uncle on the Miami River. He charted the "Village of Miami" on the south bank of the Miami River and sold several plots of land. In 1844, Miami became the county seat, and six years later a census reported there were ninety-six residents in the area. The Third Seminole War was not as destructive as the second, but it slowed the settlement of southeast Florida. At the end of the war, a few of the soldiers stayed.