They aren't really consolidated so much as they're interlocked. Many of the largest companies in Japan own stock in all of the other largest companies in Japan. It diversifies their holdings and insulates them from market fluctuations while maintaining their independence.

I was thinking of those too, but did they get that way via acquisitions or by entering new markets?

It's really a bit of everything. Some like Fuji, Hyundai, or Toyota, I believe have been historically diversifying across several different markets.

Sony did expand on some fronts via acquisitions, e.g. Sony Electronics acquiring Konica-Minolta, Sony Electronic Entertainment acquiring several studios, etc.