The European session covers 36% of the global market, making it the most dominant market in the forex industry. About 31% of it happened in London and 5% in the German markets. That's why the European session (8 PM to 5 PM GMT) is the busiest time and the market's liquidity is really high during the session.
The US market sessions come next and it's covered about 19% of the global markets. The US market is extremely important considering around 90% of the global goods and service trades use the US dollar. The market is very liquid during the US session, especially around the first 4 hours. That is because it overlaps with the European session and there are many high-impact economic data released during the time.
The Tokyo market covers around 16.5% of the forex markets with the Japanese yen dominating the majority of the Asian markets. The Asian markets have relatively low volatility, but the price movements might affect Australia, New Zealand, and of course Japan markets.