The planned $100 billion merger of Anheuser-Busch InBev and SABMiller will be a wake-up call to the overseas ambitions of Japanese brewers, which are struggling to grow at home in a saturated market with a shrinking population.

Japanese beer makers including Asahi Group Holdings and Kirin Holdings Co. hold more than 90 percent of their domestic market, but are tiny globally despite long-standing pledges to do more overseas as Japan¡¯s beer market slows.

If AB InBev and SABMiller are successful in their proposed marriage, then it will present Japanese brewers with an even more formidable global competitor.