According to the 2018 Greenwich Associates study, Citigroup and JPMorgan Chase & Co. were the two biggest banks in the forex market, combining for more than 30 percent of the global market share. UBS, Deutsche Bank, and Goldman Sachs made up the remaining places in the top five. According to CLS, a settlement and processing group, the average daily trading volume in January 2018 was $1.805 trillion.
At the end of 1913, nearly half of the world's foreign exchange was conducted using the pound sterling.[24] The number of foreign banks operating within the boundaries of London increased from 3 in 1860, to 71 in 1913. In 1902, there were just two London foreign exchange brokers.[25] At the start of the 20th century, trades in currencies was most active in Paris, New York City and Berlin; Britain remained largely uninvolved until 1914. Between 1919 and 1922, the number of foreign exchange brokers in London increased to 17; and in 1924, there were 40 firms operating for the purposes of exchange.[26]
The world then decided to have fixed exchange rates that resulted in the U.S. dollar being the primary reserve currency and that it would be the only currency backed by gold, this is known as the ‘Bretton Woods System’ and it happened in 1944 (I know you super excited to know that). In 1971 the U.S. declared that it would no longer exchange gold for U.S. dollars that were held in foreign reserves, this marked the end of the Bretton Woods System.
A swap trade involves both. Dealers buy a currency at today's price on the spot market and sell the same amount in the forward market. This way, they have just limited their risk in the future. No matter how much the currency falls, they will not lose more than the forward price. Meanwhile, they can invest the currency they bought on the spot market.

An interesting observation is that the Forex Market Hours of the Tokyo and London sessions overlap for approximately 1 hour (varies for other European countries). You can (and probably should!) use this fact to your advantage. This means that all the crosses of European currencies and the JPY will have the highest volatility at the start of the European session. So if you are trading the GBPJPY you can simply carry out a few powerful trades between 8am-9am GMT, and then you are free for the day!

More specifically, the spot market is where currencies are bought and sold according to the current price. That price, determined by supply and demand, is a reflection of many things, including current interest rates, economic performance, sentiment towards ongoing political situations (both locally and internationally), as well as the perception of the future performance of one currency against another. When a deal is finalized, this is known as a "spot deal". It is a bilateral transaction by which one party delivers an agreed-upon currency amount to the counter party and receives a specified amount of another currency at the agreed-upon exchange rate value. After a position is closed, the settlement is in cash. Although the spot market is commonly known as one that deals with transactions in the present (rather than the future), these trades actually take two days for settlement.