Say its the 18th century and South America wants tea. Britain, for example could have a monopoly on the tea trade in the area. However if multiple British companies sell in the area they will drive eachothers prices down. So the British government could only allow 1 company to trade there, or force a merger between the companies, so they can trade as a monopoly and make more money which will be payed as tax to the British government. Has this ever happened, or is there a flaw in my logic?
Yes, you are describing the (British) East India Company. A royal charter granted it a 15 year monopoly on English trade with "all countries east of the Cape of Good Hope and west of the Straits of Magellan". Also noteworthy, "at the height of its rule in India, the British East India company had a private army of about 260,000 — twice the size of the British Army".