Usually the traders are concentrated in operate within a specific market type with brokers which in turn are specialized in these markets. For example, if we want to buy or sell oil, we must trade with a broker dedicated to raw materials, but if we want to speculate on currencies, we must resort to a Forex broker for example. Originally, these brokers did not overlap as each of these financial assets are traded in different markets and in many instances these brokers are not licensed and / or lack of regulatory requirements.
However, with the passage of time these brokers have specialized and now offer a variety of services. For example, most Forex brokers also offer the possibility of trading with precious metals, contracts for difference and some even with binary options. In this way, the trader can access multiple markets from a single trading platform.
Markets have also evolved with investors and brokers. Now, we can see a cross between different markets and although we can access these markets from the same broker, each trade is an individual transaction, with its own rules and requirements according to the market.
For years, traders have traded with a single broker in several markets but through individual operations. In other words, if an investor wanted to speculate on the price action of Euro against gold, had to perform an operation on gold (with its risks and costs) and another in the euro, as well as a single transaction, so in fact the trader had to open two positions with double exposure.
This was the start of a form of trading called "cross-market" and initially was complex and risky, but the rewards were high and the trader could make successful trades based on their knowledge of independent markets.