Given the rapidly expanding nature of Chinese retail and ecommerce markets, it may not come as much of a surprise that China UnionPay is now the largest card scheme in the world. According to Datamonitor Financial, China UnionPay's branded cards account for nearly 37 percent of the global market, or 2.4 billion cards. 

However, that total is slightly skewed, as 408 million China UnionPay cards are dual-branded with Visa for transactions made outside of the country's borders. Outside of China – where the UnionPay maintains a monopoly because of government regulations – Visa and MasterCard are the two major players in the international payments card industry. More specifically, MasterCard issued more than 21 percent of the world's branded cards in 2014, while Visa issued more than one-third of branded cards.

Not much room for other stakeholders
Both MasterCard and Visa seem to have a firm stronghold on the remainder of the international market while China UnionPay has nearly complete market share in its own country. Japan Credit Bureau and and American Express, while powerful payments brands, are still struggling to gain reputable market share on a global basis. Both cards account for 1.7 and 1.8 percent of global cards issued, respectively, Datamonitor Financial added. JCB has a strong foothold in it's national Japan, and it also has strong market share in East Asian countries like Taiwan, China and South Korea. 

On the other hand, American Express has historically performed strongest in North America, but is also represented well in Latin America and in Europe. 

Visa and MasterCard to enter Chinese market
The one market that both Visa and MasterCard seemingly couldn't penetrate for years due to favorable federal regulations was China. That is about to change, though.

According to Reuters, the country will open up its market for clearing domestic bank card transactions, which would ultimately allow outside players like Visa and MasterCard to enter the market that was valued at nearly $6.5 trillion in 2014. Per the report, foreign firms will be allowed to set up their own clearing companies in China and apply to its central bank for appropriate payment processing licenses as soon as June 1. 

"Opening up the market for bank card clearing will help improve the country's card-clearing services through market competition," Reuters reported, citing an online statement from the People's Bank of China.