Best countries in these major combat sports?

Tough to say, there are great fighters all over the place. I would agree with you mostly but great boxers come out of places like Africa, Mexico, the P.I. and the Netherlands produces excellent kick boxers

MMA: definitely the ones' you said, but there are quite a few good Mexican fighters coming up now.
Kickboxing: America and Europe. However, Muay Thai is definitely ruled by Thais.

Olympic Wrestling: Us wrestlers are excellent, like Gold medalist Kurt Angle. Also Europe.
Boxing: Yeah, the Russians are dominating the heavywieght now, along with US fighters. Also central American fighters dominate lower weight classes.
Judo: Definitely Japan.
Traditional Martial ARts: Depends on the art. Japanese karate-ka dominate Shotokan tournaments, and US ones in the US. TKD has strong Korean and US competitors.

You forgot to mention the Mexicans for boxing. Off the top of my head, I've got to think they've produced the most world champions of any country, aside from probably the USA. They pretty much dominate the lighter weight classes, where the vast majority of exciting fights take place.

I think Russia should be listed with USA, Brazil and Japan under best MMA.

I agree with most of your choices.

1) MMA: USA, Brazil, Japan.
2) kickboxing including muay thai: Thailand and Holland.
3) Olympic wrestling: Aleksander karelin comes to mind (Russia)...... I agree Eastern european countries and USA.
4) Boxing: U.S. dominates heavyweights. lightweights there are alot (Cuba, Mexico, and so on)
5) Judo: it's country of origin, Japan.
6) Traditional martial arts, their countries of origin. (TKD-- Korea, Karate--Japan, Wushu--China)
7)jujitsu , it's country of origin, Japan.
Brazilian jujitsu, it's country of origin, Brazil.

1) MMA - USA. It started here, it'll end here.

2) Kickboxing- Thailand, then China (Sanshou)

3) Olympic Wrestling- USA

4) Boxing- U.S. (Rocky vs. Drago).

5) Judo- Japan

6) Traditional Martial Arts- Japan.

7) Jujutsu - Japan. Jiu-Jitsu- Brazil (big difference).