It's like this, Ambev was the original company but later became the operating name of the South American division after a merger with a European company, this resulted in InBev. Later, this merged company acquired AB, but due to regulation (anti trust laws) it had to appear like a merger rather than an acquisition. Thus the resulting corporation became the worlds largest brewing company (all brands together) Ab-InBev.
Ab had already contended with a huge loss in market share when Corona (at the time owned solely by a Mexican corp) started its steep ascent in the US market. The worldwide growth phenomenon was so rapid, that after the initial Inbev/AB merger, the best solution to avoid direct confrontation was to acquire a percentage of the Mexican Brewer. AB/Inbev gained all the HL (hectoliters - common measurement of sales performance for beer) from Corona which are now accounted for under Ab-Inbev contributing a very nice slice to the status of #1. Corona's parent company gained assurances of distribution partnerships in the US and through ought the world vs having to spend millions trying to compete. Everybody wins. (except their completion)
The trouble (or opportunity) is that brands like Brahma or Skol (some of Brazils internal leading brands, both under the Ambev umbrella ) have been getting much international attention for their great qualities, attractive packaging, and much better flavor with no lime needed. Add to that the fact that every time you mention Brazil you can't help but think of sex, (although some think of soccer, go figure) and you have the perfect candidate for the next worldwide rocket brand.
Inbev has been trying to control this since they don't want o spend more money advertising another brand in the US market or the world for that matter, but has smaller brands start to expand into these markets they eventually will not have a choice.
Granted that they control the biggest brands, but the smaller ones have a shot at retaining some market share if they capture some before Inbev starts their campaign. Might take 2-3 or even 10 years. but unless Brazilian women stop wearing those Bikinis and the country is taken over by zombies there is only one direction.