There are several ways to look at the relationships between forex trading and the stock markets, especially when considered across various countries and their markets. Another branch of consideration is forex scalping, or really scalping in any financial instrument, as it relates to methods of successful trading.
Because stocks and other financial instruments are ultimately traded based on some monetary relationship, any time a currency pair has a price change, there is going to be a similar response in the stock market prices. Rarely will the stock markets drive a currency price. It is possible that futures prices on a currency can be involved in pricing structures, though.
Most currency prices are impacted to the largest degree by the Central Banks of each country whose currency it represents. Some currency is used throughout an entire region of the world, such as the Euro, and that is driven by a collection of countries represented by their own version of a central bank.