Question: Alexander Fulton founded which city that had a mild subtropical climate that was required for agricultural production using slave labor? 

Context paragraphs:
Climate of Bilbao: Bilbao and its metropolitan area has an oceanic climate according to the Köppen climate classification (" Cfb") with mild winters and warm summers.  According to the Troll-Paffen climate classification, Bilbao has a temperate climate and according to the Siegmund/Frankenberg climate classification, Bilbao has a subtropical climate.  According to the European Environment Agency, Bilbao lies within the Atlantic biogeographical region.  The climate of Bilbao and the rest of the north-western part of Spain (the so-called Green Spain) is different from the rest of the country, characterized by a higher amount of rainfall and precipitation days, fewer sunshine hours and mild temperatures, in summer comparable to northern half of Europe with temperate climate.

Climate of Valencia: Valencia and its metropolitan area have a hot-summer Mediterranean climate (Köppen climate classification: "Csa") with very mild winters and long warm to hot summers.  According to Troll-Paffen climate classification, Valencia has a "warm-temperate subtropical" climate ("Warmgemäßigt-subtropisches Zonenklima") and according to Siegmund/Frankenberg climate classification, Valencia has subtropical climate.

List of locations with a subtropical climate: This list of locations with a subtropical climate specifically lists locations considered within the subtropics.  The subtropics are geographic and climate zones located roughly between the Tropic of Cancer and Tropic of Capricorn and the 40th parallel in both hemispheres.  Subtropical climate regimes can exist at high elevations within the tropics, such as across the Mexican Plateau and in Vietnam and Taiwan.  Six climate classifications utilize the term to help define the various temperature and precipitation regimes for the planet Earth.  Using the Trewartha climate classification eight or more months of the year within the subtropics have an average temperature at or above 10 °C .  The Köppen climate classification instead classifies the warmest month above 22 C and the coldest above 0 C or -3 C depending on preference.

Alexander Fulton (Louisiana): Alexander Fulton (died c. 1818) was a merchant, planter, and local politician originally from Washington, near Pittsburgh in western Pennsylvania, who in 1805 founded the city of Alexandria, Louisiana, which he named for himself.

Climate of Lisbon: Lisbon and its metropolitan area has a Subtropical-Mediterranean climate (Köppen climate classification: "Csa"), with short and very mild winters and warm summers.  According to Troll-Paffen climate classification, Lisbon has a "warm-temperate subtropical" climate ("Warmgemäßigt-subtropisches Zonenklima").  According to Siegmund/Frankenberg climate classification, Lisbon has a subtropical climate.

Climate of Missouri: Missouri generally has a variety of seasonal humid subtropical climate (Köppen climate classification "Cfa"), with cool winters and long, hot summers.  In the southern part of the state, particularly in the Bootheel, the climate borders on a more mild-type humid subtropical climate (Köppen "Cfa"), and in the northern third, the state transitions into a humid continental climate (Köppen "Dfa").  Because of its location in the interior United States, Missouri often experiences extremes in temperatures.  Lacking either large mountains or oceans nearby to moderate its temperature, its climate is alternately influenced by air from the cold Arctic and the hot and humid Gulf of Mexico.  St. Louis is surrounded by 2 rivers.  The mississippi river and the Missouri river.  With these 2 rivers surrounding St. Louis it can cause changes in the weather pattern.

Plantations in the American South: Plantations were an important aspect of the history of the American South, particularly the antebellum (pre-American Civil War) era.  The mild subtropical climate, plentiful rainfall, and fertile soils of the American Southeast allowed large plantations to flourish; where large numbers of workers, usually Africans held captive for slave labor, were required for agricultural production.

Climate of Rome: Rome and its metropolitan area has a Mediterranean climate (Köppen climate classification: "Csa"), with mild winters and hot summers.  According to Troll-Paffen climate classification, Rome has a "warm-temperate subtropical" climate ("Warmgemäßigt-subtropisches Zonenklima").  According to Siegmund/Frankenberg climate classification, Rome has a subtropical climate.

Environment of Florida: The environment of Florida in the United States yields an array of land and marine life in a mild subtropical climate.  This environment has drawn millions of people to settle in the once rural state over the last hundred years.  Florida's population increases by about 1,000 residents each day.  Land development and water use have transformed the state, primarily through drainage and infill of the wetlands that once covered most of the peninsula.

Climate of Barcelona: Barcelona and its metropolitan area have a humid subtropical climate (Köppen climate classification: "Cfa"), bordering a Mediterranean climate ("Csa") with mild winters and hot summers.  According to Troll-Paffen climate classification, Barcelona has a "warm-temperate subtropical" climate ("Warmgemäßigt-subtropisches Zonenklima").  According to Siegmund/Frankenberg climate classification, Barcelona has a subtropical climate.  Barcelona is located on the eastern coast of the Iberian Peninsula, so Atlantic west winds often arrive in Barcelona with low humidity, producing no rain.  The proximity of the Atlantic, its latitude, and the relief, are the reasons why the summers are not as dry as in most other Mediterranean Basin locations.

Supporting paragraphs: Alexander Fulton (Louisiana) Plantations in the American South
Answer: Alexandria, Louisiana