Question:  Fort Metal Cross a trading post for the slave supply was crucial to supply labor for what country

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Dutch Slave Coast: The Dutch Slave Coast (Dutch: "Slavenkust") refers to the trading posts of the Dutch West India Company on the Slave Coast, which lie in contemporary Ghana, Benin, Togo and Nigeria.  The primary purpose of the trading post was to supply slaves for the plantation colonies in the Americas.  Dutch involvement on the Slave Coast started with the establishment of a trading post in Offra in 1660.  Later, trade shifted to Ouidah, where the English and French also had a trading post.  Political unrest caused the Dutch to abandon their trading post at Ouidah in 1725, now moving to Jaquim, at which place they built Fort Zeelandia.  By 1760, the Dutch had abandoned their last trading post in the region.

Bowlin's Old Crater Trading Post: Bowlin's Old Crater Trading Post is a former trading post which was located along historic U.S. Route 66 in Bluewater, New Mexico.  The trading post was built in 1954 by Claude Bowlin.  Bowlin had traded with local Navajo since 1912, and he built his first trading post at the site in 1936.  The store's name came from a volcanic crater that drew tourists to the area.  While the trading post initially served the Navajo, it soon served tourists as well due to increased traffic on Route 66.  Inspired by his success, Bowlin built a chain of stores throughout New Mexico, which became Bowlin Travel Centers, Inc. In 1954, Bowlin replaced his original trading post with the current building.

Fort Alexander, Manitoba: Fort Alexander -"Sagkeeng" Ojibway (mouth of the river) is a community in Manitoba, Canada, located on the Sagkeeng First Nation, on the south bank of the Winnipeg River.  The Sagkeeng area, or the mouth of the Winnipeg River, was originally settled with native camps used for fishing, hunting, and trade.  During the fur trade era, La Vérendrye built a trading post, named Fort Maurepas, on the north side of the river; this post was abandoned near the end of the French period.  In the year 1792, a clerk for the North West Company, Toussaint Lesieur, built a post on the south side, which became an important provisioning post for the canoe brigades.  Bags of pemmican, brought from the North West Company's posts on the upper Assiniboine, were stored here and taken as needed by the canoe brigades passing between Grand Portage (later, Fort William) and the far northwest.  This post was usually referred to as Fort Bas de la Rivière, because of its location at the bottom of Winnipeg River, and it seems to have functioned as the capital of the Company's Lake Winnipeg district.  The Hudson's Bay Company operated its own post here for a few years between 1795 and 1801.  In 1807, the North West Company partner Alexander MacKay rebuilt the post on a nearby site.  Beginning in 1808, the new post was known as Fort Alexander.  After the Northwest and Hudson's Bay Companies merged in 1821, Fort Alexander was operated as a trading post for the natives in the region.

Fort Robidoux: Fort Robidoux, a fur trading post also known as Fort Uintah and Fort Winty, was located at the junction of the Uintah and Whiterocks rivers in the Uinta Basin of northeastern Utah.  It was founded in 1832 after Antoine Robidoux bought out the Reed Trading Post that had been in operation at that site since 1828.  Robidoux had traded for beaver pelts in the Uintah Basin region as early as 1824.  By 1828 he had established his first trading post in the intermountain corridor of the western slopes of the Rocky Mountains on the Gunnision River near present-day Delta, Colorado.  Robidoux took out Mexican citizenship and married Carmel Benevedes, the adopted daughter of the governor of New Mexico, that same year.  This enabled him to obtain a Mexican trading and trapping license.

Fort Metal Cross: Fort Metal Cross, originally Fort Dixcove, is a military structure in Dixcove, Ghana.  It was built commencing in 1683 by the English Royal African Company as a trading post for the gold and the slave trade, though construction didn't finish until 1698 due to ongoing hostilities with the local people.  Brandenburg-Prussia started building Fort Groß Friedrichsburg about 15 km west of Dixcove in 1683, (now Princes Town) in the colony of Brandenburger Gold Coast but it was not completed until the 1690s.

Old Fort Providence: Old Fort Providence, located near the mouth of Yellowknife Bay, Northwest Territories, Canada, was one of the first fur trading outposts on Great Slave Lake.  Peter Pond of the North West Company first proposed trading with the Dene around Great Slave Lake in 1786.  In 1789, Alexander Mackenzie initiated a period of trade with the Yellowknives and Tłı̨chǫ (formerly known as Dogrib) Dene and instructed his assistant, Laurent Leroux, to start a trading post in this area.  The post was not a major centre for fur trading and was used primarily as a supply centre for other, more important trading posts or expeditions.  It served, for example, as a base of supply for Sir John Franklin's Coppermine Expedition towards the Arctic Ocean in 1820.  It was located within a productive fishery used for generations by the Dene around Yellowknife Bay and helped supply meat and fish for traders at Great Slave Lake.  The Hudson's Bay Company took over the post in 1821 after the demise of the North West Company, but the settlement was in decline and it closed in 1823.  The buildings have long since decayed but the ruins were excavated in 1969-1971.

Roop's Fort: Roop's Fort, also known as Roop's Trading Post, Fort Defiance, and Roop House, is a historic building in Susanville, California.  The building, which was built in 1854 by Isaac Roop, was the first building built by white settlers in Lassen County.  The fort was originally a trading post for westbound migrants and was the first post west of Fort Hall in Idaho.  The building also served as the capitol of the short-lived Nataqua Territory, a territory created in 1856 to avoid California tax collectors.  The territory was incorporated into Roop County, Nevada, named for Isaac Roop, in 1861.  California and Nevada entered into a border dispute known as the Sagebrush War over the Susanville area in 1863, and Roop's Fort served as a fort for the Nevadans during the skirmish.  California won the war, and Roop's Fort became part of Lassen County in 1864.

Fort Platte: Fort Platte was a stronghold and trading post established by Lancaster Lupton that was active between 1840 and 1846.  The fort competed with Fort Laramie which was only one mile away and quickly surpassed it due to a superior supply system.  In 1842, due to economic losses, Lupton had to sell the fort and it was bought by the successful fur trading firm Pratte and Cabanné who managed it from 1843 to 1845.  In 1845, Pratte and Cabanné moved operations to Fort Bernard to try to capture traffic traveling west on the Oregon Trail before it reached Fort Laramie.

Atlantic slave trade: The Atlantic slave trade or transatlantic slave trade involved the transportation by slave traders of enslaved African people, mainly from Africa to the Americas, and then their sale there.  The slave trade used mainly the triangular trade route and its Middle Passage, and existed from the 16th to the 19th centuries.  The vast majority of those who were enslaved and transported in the transatlantic slave trade were Africans from central and western Africa, who had been sold by other West Africans to Western European slave traders (with a small number being captured directly by the slave traders in coastal raids), who brought them to the Americas.  The South Atlantic and Caribbean economies especially were dependent on the supply of secure labour for the production of commodity crops, making goods and clothing to sell in Europe.  This was crucial to those western European countries which, in the late 17th and 18th centuries, were vying with each other to create overseas empires.

Fort Apollonia: Fort Apollonia is a fort in Beyin, Ghana.  The name Apollonia was given to the area by a Portuguese explorer who sighted the place on the Feast of Saint Apollonia, 9 February.  The Swedes established a trading post at Apollona as part of the Swedish Gold Coast between 1655-1657.  In 1691, a British trading post was erected at this site, which between 1768 and 1770 was extended into a fort.  After the abolition of slave trade, the fort was abandoned in 1819, but it was again occupied from 1836 onwards.

Supporting paragraphs: Fort Metal Cross Atlantic slave trade
Answer: European