Three, and the ones that aren't around any more weren't always merged, but simply closed shop.
Not necessarily the case for truck manufacture -- see the variegated history of
White Motor Company, for one.
How old is
Kia Motors? Wiki says its earliest incarnation was 1944 as a tubing and bike parts manufacturer. It set up shop in the US in 1992. How about
Daewoo? Twenty-three years younger. And making cars for GM now... since 2001. Seems an example of capacity going on the market and being bought up.
All this hooraw and going through changes looks like free markets to me, particularly Daewoo's collapse as a conglomerate and its rebirths as sundry spinoff companies still doing what they started out as. This kind of thing goes on in free markets when a government makes a point of not muddying the waters. I'm not seeing a "reduction of competition" here. I get the feeling globalization is making such "reduction" an impossibility, as
any entrepreneur can hurl himself at
any market, anywhere on the globe these days.
Lemonade stands and auto manufacturing still obey the laws of economics.